Docks and other floating overwater structures can have structural and biological impacts to nearshore marine environments.
Piers and floats block the sunlight that eelgrass requires to grow. Loss of eelgrass cover in areas under and adjacent to docks may result from direct shading, piling installation, and boat traffic (i.e., propeller scarring).
Declines in eelgrass coverage could have important consequences for those marine animals that utilize eelgrass as habitat, and may also alter some of the physical properties of the habitat itself such as changes in water circulation patterns and reduced sediment stability and retention. Research in Puget Sound has also shown that out-migrating juvenile salmon avoid traveling under docks; requiring more energy to travel out around the docks, which also places them into deeper waters, where the risk of predation is higher.
The area of eelgrass loss associated with any individual dock can be relatively small; however the cumulative impacts and fragmentation of eelgrass beds is likely significant.
Mooring buoys, marinas, community docks are all viable alternatives to individual docks. Use of these alternatives greatly reduces the environmental, aesthetic and navigational impacts of individual docks.