Between 1885 and 1983, development, draining and dredging along the lower Columbia River converted about 7,000 acres of marshland into farmland through dike-building that was pursued until the 1930s. After the 1930s, most of the development of estuaries and wetlands involved dredging and filling to deepen channels for ports, piers, boardwalks and buildings. By the 1970s, between 50 and 70 percent of Pacific Northwest estuary wetlands had been reduced through diking and dredging These projects eliminated some of the wetlands where smolts linger, grow and acclimate before heading out to the ocean. Salmon species such as chum, coastal coho and chinook seem particularly dependent on estuaries to accustom them to saltwater and prepare them for their lives at sea. But increasing information about the role of coastal wetlands and estuaries led to increased federal and state rules about building new dikes or dredging and filling activities.
Pollution also poses a threat to estuaries.
Storm water washes off everything from parking lots in Portland to farm fields in Silverton and eventually washes into estuaries as well. Jane Lubchenco, a marine ecologist at Oregon State University, said the excess of nitrogen and phosphorus from fertilizer runoff, waste from people and animals and the burning of petroleum products appears linked to large, oxygen-robbing blooms of algae. These blooms can sicken humans and kill fish, she said. Yet the dangers to estuaries are balanced by efforts on their behalf. Some of the most aggressive efforts on behalf of habitat restoration are taking place along coastal estuaries.