In the early 1900s, the native Olympia oyster was harvested in Samish Bay, but because Olympia oysters were difficult to culture, their populations declined in the 1920s from overharvesting. In 1921, the Pacific oyster from Japan was introduced to Samish Bay and became the dominant oyster species cultured on the West Coast. It grows well in the Pacific Northwest but seldom reproduces successfully there because of cooler water temperatures, so oyster seed was brought annually from Japan for nearly forty years, while today the shellfish industry relies on modern hatcheries for seed production. Samish Bay oyster production peaked in the early 1940s at more than 60,000 gallons of shucked meat annually, then pollution from pulp mills diminished production through the mid-1960s until effluent standards were adopted for the pulp and paper industry through efforts by the shellfish industry and concerned citizens. Work continues to rebuild Olympia oysters in Samish Bay and other historic grounds around Puget Sound, while pollution from storm water runoff, agriculture, forest practices, animals in streams, failing septic systems, erosion, boat sewage holding tanks, and improper waste disposal continues to threaten water quality throughout the watershed. Pacific oysters and Manila clams are now cultured extensively in Samish Bay, and geoducks, horse clams, butter clams, cockles, and native littleneck clams are also harvested recreationally. These bivalves are filter feeders that consume plankton and can also concentrate pollutants in the water. Residents in surrounding communities have worked to improve conditions by repairing and replacing failing septic systems and developing farm plans to address agricultural pollution. For a century, oyster clusters were farmed on the firm, sandy bottom areas of Samish Bay and shucked in processing facilities on Chuckanut Drive and on Samish Island. Growers now produce single oysters from hatchery seed, farming them either on the bottom or off the bottom in plastic mesh bags with buoys or in floating cages that tumble the oysters in the waves. Manila clams are farmed in firm, sandy substrate under four-foot-wide predator-exclusion nets installed at low tide, seeded with hatchery-produced baby clams, and typically take about three years to reach market size.