Publication Summary

This report comprises the "Lake Chapter" of Washington's 1994 305(b) report, and completion of this report partially fulfills Washington's obligations under sections 305 and 314 of the Federal Clean Water Act.

This report comprises the "Lake Chapter" of Washington's 1994 305(b) report, and completion of this report partially fulfills Washington's obligations under sections 305 and 314 of the Federal Clean Water Act.

Ecology's Lake Water Quality Assessment (LWQA) Program was established in 1989 to gather water quality information from significant, publicly-owned lakes, to assess the trophic status of monitored lakes, and to educate the public about lake processes and lake protection. Monitoring is conducted by Ecology staff and by a corps of volunteers. Ecology staff collect water samples and profile data in May and August. Water samples are analyzed for total phosphorus, total nitrogen, and chlorophyll a. Profiles include temperature, pH, dissolved oxygen, and conductivity. Volunteers measure Secchi depth and surface water temperature at one lake station every two weeks from May through October. During 1992 and 1993, a total of 100 lakes were monitored for Ecology's LWQA program. Of these lakes, 78 were monitored by volunteers and Ecology staff, and 22 were sampled by Ecology staff only. Most lakes sampled only by Ecology staff were selected to support Ecology's watershed approach to water quality management.

There are approximately 1,000 significant, publicly-owned lakes in Washington that could be assessed for Ecology's LWQA Program. In addition to assessments from Ecology's LWQA program, assessments from other sources were included in this report if the information was published and the data were collected within 1989-1993. In all, trophic state assessments for 174 significant, publicly-owned lakes are listed in this report. Of the assessed lakes, 34 were oligotrophic, 80 were oligo-mesotrophic or mesotrophic, 58 were meso-eutrophic or eutrophic, and 2 were hyper-eutrophic. Of 17 lakes which had five consecutive years of Secchi depth data, two lakes had statistically significant improving trends in water clarity, and one lake had a statistically significant decreasing trend in water clarity.

Lakes monitored for Ecology's LWQA Program from 1989 to 1994 were ranked in order of their need for eutrophication management based on the ranks of variables descriptive of susceptibility to eutrophication, water quality, public value, and change in phosphorus concentration. Fifteen lakes were identified as high priority lakes for eutrophication management. An additional 12 lakes with good water quality were identified as high priority lakes for protective management.

As required, this report also includes descriptions of programs which control pollution into lakes, descriptions of lake restoration techniques, and a discussion of acid deposition in Washington lakes. Aquatic plant management in Washington lakes is also discussed.