A bottom of hard-pan clay lies about 35-50 feet below the river surface in the northern half of the Detroit River. In the southern half, a bottom of limestone bedrock slopes upward from Ecorse south and across the river mouth. Bedrock reaches the water surface in several areas such as Stony Island. This explains the larger number of islands and stone quarries in the lower river.


The earliest inhabitants in the lower river were Native Americans dating back to about 3000 years BC. They settled in the area because of the readily available food such as wildfowl, fish, wild rice and native fruit trees along the shore. The 1813 map shows six Native American villages in the lower river.

Maps that date back to 1796 show the area between Elba Island and the main island as a shallow marsh varying in width from 1/4 mile to about 1/2 mile. The 1876 map shows the current Grosse Ile Nature Area with no owner but a stone quarry in the middle section. The 1916 map based on a 1903 survey shows the first human alteration of the area with a causeway and road running down the eastern side of the marsh. The road is now known as East River Road.

In 1926, the Aircraft Development Corporation was awarded a $300,000 contract by the Navy Department for construction of the world's first all metal airship. The ADC purchased the south end of the island from the R.E. Olds family for construction of a hangar and landing field. In 1927, the Navy Department assigned the property to the Naval Reserve and began construction on a seaplane base on a shallow island in the southern edge of the property. Construction involved placing a causeway from East River Road through the shallow channel to the island with two causeways extending to the landing field.

The year 1929 saw the completion of the first all metal airship, the seaplane base and the dedication of the 375 acre Naval Reserve Aviation Base. The air station was expanded to 604 acres in 1942. The Department of Defense acquired the eastern portion of the Air Station about 1952 and completed construction of the Nike-Ajax Missile site in 1955. The missile site was part of the air defense of Detroit during the cold war. Construction of the site required filling several more acres of the original shallow river channel. In the mid 1930s the lowest river levels in modern history were recorded and in an aerial picture of the area the "bay" appeared as a wet meadow. A narrow stream ran perpendicular to the East River Road causeway.

The missile site was abandoned in 1962; the air station was declared obsolete and abandoned in 1969. The Environmental Protection Agency acquired the site in 1975 for scientific studies and the structures were demolished between 1991 and 1993. The GINLC was given stewardship of the site in 1993 to develop a natural area for the community, thereafter called the Grosse Ile Nature Area.

The water level of Lake Erie, the Detroit River and Gibraltar Bay were all above average during the last three decades of the twentieth century. From the late 1970's through the early 1990's these waterways experienced the highest water levels of the century, with maximum water levels reached in 1986 (max = 174.3 m or 571.9 ft). In those years Gibraltar Bay was a body of open water with relatively low vegetation. Prior to this period and through a portion of it as well, the river also experienced relatively high pollution rates. Compliance with the Clean Water Act of 1972 and increased control of sewage-storm water releases later in the century began to improve the water quality of the river-lake system. The invasion of the zebra mussels in the late 1980s also created change in the ecosystem. In removing particles from the water these voracious filter-feeding organisms have dramatically increased water clarity.

In the late 1990s water levels in Lake Erie and the Detroit River began to drop. Low precipitation and increased evaporation from 1997 to 1998 brought water levels closer to the long-term recorded average (mean = 174.1 m or 571.2 ft). By 1999 however, water levels actually decreased to below average for this area for the first time since the 1960s. Low water levels have continued into the current decade. The combination of high water quality and clarity, warm temperatures and shallow water in Gibraltar Bay has led to conditions that are ideal for the growth of vegetation. Historical records indicate that vegetation in the bay area was quite common over the last several hundred years, particularly during low water periods. Examples include the 1960's and 1930's when the lowest water levels of the twentieth century occurred in 1934 (low = 173.2 m or 568.2 ft).

There is considerable uncertainty as to the effect of global climate change on Lake Erie water levels. Natural fluctuations of water levels over the last century have varied over a range of 2 meters (6.6 ft). Estimates for additional water reduction due to climate change range from 1 to 2 meters (3.3 ft to 6.6 ft). Reductions of this magnitude have the potential to significantly change the shoreline of Lake Erie.

The vegetation in Gibraltar Bay is a mix of native and non-native species. Only a few relevant species will be discussed in this report.

     WILD RICE (Zizania aquatica)

G. A. Cooper, Courtesy of Smthsonian Institution

One of the primary reasons for the Native American presence in the lower Detroit River was the abundance of wild rice and the diversity of wildlife that this source of food attracted. Wild rice or "manoomin" as the native people called it was a staple in their own diet as well. It is actually a grain that is high in protein, carbohydrates, vitamins and minerals, but low in fat. The wild rice grows well in shallow waters like a protected bay with low current and little competition from other plants. The wild rice helps maintain water quality by binding loose soil and tying up excess nutrients. In the process it reduces algae blooms and improves water clarity.

Although wild rice was common in the lower river area before extensive industrialization, it is now considered rare in the state of Michigan and is a state threatened species. With the advent of shoreline destruction due to development, high water levels and water pollution few of the native wild rice beds have survived. Since the wild rice is considered an important wildfowl food source it is sometimes planted to improve wildfowl habitat.

In the spring of 2004 the GINLC tried to restore wild rice at the eastern side of Gibraltar Bay, twenty feet offshore from the Nature Area, not far from the amphitheatre. Stakes were driven into the corners of a 25 by 50 foot area which was then enclosed with chicken wire to keep wildfowl from eating the seeds and any of the young plants that might sprout. Some seeds were also scattered twenty feet offshore from the western shore, but without protection. No wild rice sprouts or plants have been observed in either area. Although the wild rice seeds may lay dormant for five years, it is unlikely that they will sprout in the near future because of the presence of flowering rush, the main vegetative species currently in the bay.

     FLOWERING RUSH (Butomus umbellatus)

Richard A. Howard Image Collection, Courtesy of Smthsonian Institution

In the last eight years this plant has become the most common emergent vegetation in Gibraltar Bay and is now present throughout most of the shallow water. It is a non-native species from Europe that came to the Midwest as an ornamental garden plant. It is found in shallow water with a muddy bottom. It does not grow in water with much current or wave motion. Hence, the channel from the east and the area south of the seaplane pad and air base has remained free of its growth.

Flowering rush invades areas that are not occupied by other plants then gradually crowds out native species. It is now also found in the shallow, quiet water near Stony Island wetlands elsewhere in the lower river and western Lake Erie. Due to its almost universal coverage and extensive root system, control is virtually impossible. Herbicide treatments are generally not effective. Boats, moving water and ice can all transport pieces of roots that readily form new plants. Physical disturbance and attempted removal can also encourage additional growth and spreading since new plants will develop from root fragments that remain or break off and migrate to new areas. The roots and stems are also favored by muskrats for building their houses, locally spreading the plant. Many of these are visible in the bay just west of the East River Road causeway.

     AMERICAN LOTUS (Nelumbo lutea)

Photo by Margarete Hasserodt

The American lotus is a perennial aquatic herb. It grows in shallow waters and is an indicator species for high water quality. At one time it was plentiful all along the shallow waters of the Lake Erie shoreline and like wild rice was a food source for Native Americans. With industrialization and development of coastal wetlands along the river in the 1900s it became an endangered species in the state. Although it is now recovering in the Great Lakes it is still under state protection as a threatened species, subject to rigorous regulation. In 2004 the American lotus blossom was chosen by the state as a symbol of Michigan's clean water. The lotus has a beautiful large pale yellow flower with large (12-18 inch) round leaves that are emersed above the water or floating on it.

The American lotus bed situated south of the airport causeway and the abandoned seaplane pad appeared there naturally around 1999. Blooms were first documented there by conservancy members in 2001. It is surmised that the seed pods which float may have blown in from the beds at Lake Erie Metropark, or further south from the Monroe area during a strong south wind. The seed pods may have also arrived after having been frozen in ice. As ice flows break loose due to wind and water level changes, they could have been driven north and into the Bay, again by winds from the south that eventually drove them against the shore line.

Another possibility is that the lotus bed has been there for many years but high water and pollution caused the plants to lie dormant and are now recovering. It has been reported that lotus seeds can remain viable for decades. With the return of cleaner water at lower levels, enough light penetrated to the bottom for the seeds to germinate and for the plants to reemerge. It is also possible that the seeds had been washed in many years ago and again, the cleaner and lower water provided enough light penetration for germination. The lotus bed, which was roughly 60 feet in diameter when observed in 2001, expanded to an area approximately 400 feet in diameter in 2006. Although significant in size, aerial photos show that the lotus bed covered a small area of Gibraltar Bay relative to the widely distributed flowering rush.

In 2002, with state permits secured from the DNR, the Monroe Lotus Club collected American Lotus seed pods that had blown up along the shoreline in Monroe. In May of 2002 the GINLC with guidance from the Monroe Lotus Club planted 114 seeds in the area around the Grosse Ile Nature Area. After embedding the seeds in clay to prevent wildfowl from quickly eating them, fifty of the seeds were planted at each of two locations at the southeast end of the Nature Area. The first set was planted just offshore from the east-facing public observation area; the second set was planted offshore from the observation area facing west. The remaining 14 seeds were planted in the enclosed marsh to the west of the airport causeway that leads to the seaplane pad. The only growth observed from these plantings has been a few plants in the area along the western shore at the southeast tip of the Nature Area. The first blossom appeared here in the summer of 2006.

In 2006 several leaves were also observed in the shallow water just east of the causeway to the seaplane pad. These have not yet flowered and are presumed to have resulted from seeds blown over from the original bed.

Dr. Bruce Manny, a fisheries expert at the U.S. Geological Survey's Great Lakes Science Center, calls the entire Gibraltar bay "a productive nursery habitat for numerous sport fishes during their first summer of life, including largemouth and smallmouth bass, northern pike and yellow perch". He noted that "the sandy beach on the southeast side of Gibraltar Bay is one of the very few reported nursery areas for lake sturgeon in the Detroit River."

In the summer of 2005 a DNR fish stocking crew surveyed Gibraltar Bay. Andrew Hartz of the Michigan DEQ reported finding "young of the year perch and bluegill". He noted, "Due to the shallow nature of this bay, with some current coming through it, it is a top five spot in the lower river for ecological productivity …rivaled only by the marsh and shallow water surrounding Humbug Island, Stony Island and the Pt Hennepin marshes".

The importance of local wetlands to the ecology of the lower river and the Great Lakes as a whole can not be underestimated. In the U.S. loss of wetlands and the degradation of habitats since the 1970s have been a leading cause of species extinction. In our region the moderate climate around Lake Erie allows for an ecosystem that scientists consider the most diverse and productive in the Great Lakes watershed. The Great Lakes coastal wetland provides a habitat for mammals, waterfowl, shorebirds, songbirds, reptiles, amphibians, fish, insects, crustaceans, and numerous plant species.

The wetland "nurseries of life" provide spawning and nursery habitat, protection for juvenile fish and feeding areas for predators, including many recreational and commercial fish species. Wetlands also function as water quality filters, absorbing excess nutrients, sediments and pollutants in storm water run-off. As such it is also a fragile ecosystem that can be overloaded and stressed. Non-native species of plants and animals can work to destroy the habitat needed for ecological diversity. These valuable wetlands need to be monitored, protected and maintained.

It is clear from historical records that Gibraltar Bay is a Great Lakes coastal wetland that has been directly affected for centuries by variations in the water levels of Lake Erie. Relatively shallow areas of the lower Detroit River become marsh-like in times of low water, as was evident in the 1930s. In times of high waters, as in the 1980s and 1990s, plants that thrive in shallow water become dormant, only to reappear when conditions become more suitable. The American lotus bed that is currently thriving in Gibraltar Bay just south of the seaplane pad appeared there quite naturally. No activities of the GINLC influenced the emergence of the American lotus. The main vegetative species currently growing in the shallow wetland of Gibraltar Bay is the Flowering rush. It is a non-native species that is now dominating the wetland to the exclusion of native species. The GINLC did not introduce and would not have considered introduction of a non-native species like Flowering rush to the bay, or any other area under its stewardship. In partnership with the EPA and GI Airport, the conservancy will continue to steward the Grosse Ile Nature Area and its associated wetlands in an ecologically responsible manner.

Ad Hoc Committee on Gibraltar Bay - February 6th 2007
Update: October 23rd 2007