Shoreline or Over-water Construction changes in the shoreline that alter the absorption of wave energy may erode the bottom and also increase turbidity. Structures built over the water prevent eelgrass from getting enough light to grow. Seawater Cooling Using seawater to cool generators in power plants kills eelgrass with higher temperatures. Spilled Oil causes eelgrass plants to lose their leaves. Decreased Water Quality Increased nutrient-loading causes excessive epiphyte growth on eelgrass blades, blocking out light.
Herbicides used on coastal land can kill or damage eelgrass.
Invaders Japanese oyster seed brought to Washington in 1902 was packed in Japanese eelgrass - Zostera japonica, Sargassum seaweed and Spartina. These foreign plants soon took hold, crowding and displacing native plants. In the 1940's, well-meaning duck hunters and farmers planted Spartina, also known as Cordgrass, in many of Washington's river deltas in order to stabilize dikes and provide duck habitat and cattle graze. Since then, Spartina has spread rapidly and is now a major threat to our coastal ecosystems. Because eelgrass meadows occur in shallow water, they are subject to loss and degradation from shoreline development and pollution.