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Filling has severe effects on wetland areas, completely destroying them and eliminating all their beneficial functions. It occurs primarily in urban areas to convert wetlands to urban and industrial land use. Filling often accompanies dredging, especially for the development of harbors. Dredging involves the removal of accumulated sediments from the bottom of waterways to maintain adequate depth for safe and efficient vessel operations.
Navigation-related dredging has impacted the St. Clair River and Lake St. Clair system by altering flow regimes and replacing productive shoal-water habitat with less productive channel habitat. Navigation-related dredging in the lower St. Clair River and Lake St. Clair began in 1873 and intensified with the construction of the St. Lawrence Seaway in the late 1950s. This dredging increased the minimum channel depth to its current depth of 27.2 ft (8.3m). Dredging for the lake's navigation channel has affected water levels, permanently lowering the levels of lakes Huron and Michigan by almost 1 foot (0.3 meters). The navigation channel bisects Lake St. Clair in a northeast-southwest direction between the St. Clair Delta and the Detroit River .
Together, dredging and filling can completely destroy marshes, and impact adjacent marshes by increasing sediment loading, reducing habitat diversity, altering natural flow patterns, and changing nutrient regimes and plant communities.
For more information, see: Habitat Assessment, Section V (PDF)