Skip to main content
King County logo

Relatively little is known about the use of floodplains by salmon and trout compared to our knowledge of forested and urbanized areas. The most common species found in agricultural areas (outside of the mainstem rivers) include coho salmon and cutthroat trout, although a few juvenile chinook have been detected.

The vast majority of watercourses in the county's agriculture areas are too flat for spawning activities, and it is likely that these waters offer habitat for the rearing of juveniles, overwinter refuge, and for the transit of pre-spawn adults. In addition, the relative importance of these habitats for the various life stages of these species is unknown. It is also unknown whether the profusion of reed-canary grass provides positive or negative effects on salmonid populations, or if the accumulation of sediment has negative consequences for the fish.

ADAP staff feel that a well-considered approach to agricultural watercourse maintenance will result in both the means to maintain agricultural watercourses without harming existing habitat—or even to improve the habitat—but also to vastly improve our knowledge of chinook and other salmon species in floodplains. Staff are routinely looking for the presence and absence of salmon and trout life stages in various habitats and are measuring important water parameters such as temperature, dissolved oxygen, turbidity, electrical conductivity, and pH. In addition, the function of riparian zones and the effects of various alterations to these riparian zones are being observed. A major goal of ADAP is to determine which riparian zone alterations will result in a cost-effective yet effective mitigation for watercourse maintenance.

For questions about the Agricultural Drainage Assistance Program or ADAP, please contact Brian Sleight, Supervising Engineer, King County Stormwater Services Section.