Phosphorus reduction by dilution and shift in fish species in Moses Lake, WA

Abstract

Water quality over most of the area of Moses Lake improved greatly over a 25-year period (1977-2001) due largely to the addition of large quantities of low-nutrient Columbia River water as well as changed irrigation practices and diversion of wastewater. The oligotrophication of Moses Lake from hypereutrophy to borderline mesotrophy was accompanied by a marked shift in fish populations, determined by creel census and biological surveys that included electrofishing and gill netting. The catch fraction of panfish (crappie and bluegills) decreased markedly; largemouth bass decreased to a lesser extent, while smallmouth bass, walleye and brown bullhead increased several-fold. These population shifts are consistent with observations elsewhere in response to oligotrophication and piscivory. © 2009 Copyright by the North American Lake Management Society.