Sixteen years ago the city initiated a volunteer effort led by the Pierce Conservation District to monitor the water quality of the city’s lakes to evaluate trends and compare the data against state water quality standards.
Initially only three of the city’s six lakes – American, Gravelly and Louise – were monitored annually. Lake Steilacoom was added to the list in 2004 and Waughop Lake was added in 2011.
Carp Lake is also monitored when it has water.
Last year the city hired WEST Consultants, Inc. to analyze the conservation district’s data collected since 2000. The purpose was to determine whether the makeup of the lake water has changed over time.
Overall the data showed little change in the water quality from prior years, according to the report.
Each of the city’s six lakes showed a warming trend during the summer, when temperatures are hotter, and cooler temperatures in the winter, which is to be expected.
The lakes also registered decreased oxygen levels, and saw year-to-year increases in water clarity, but overall there were no clear annual trends regarding dissolved oxygen levels, temperature fluctuations or alkalinity, according to the report.
A number of factors like size and depth, as well as rainfall and runoff from nearby properties affect the quality of our lake water.
Findings from the report included:
- Alkalinity remains relatively uniform in most lakes, but are significantly decreasing in American and Waughop Lakes. Alkalinity is a measure of a lake’s ability to neutralize acids – which is important as it relates to aquatic plant and animal life.
- Overall chlorophyll_a decreases in American Lake, Gravelly Lake, Lake Louise and Carp Lake are statistically significant. Chlorophyll_a is a measure of the amount of algae growing in the water.
- Dissolved oxygen levels are statistically uniform in all lakes, and show no year-to-year variations. Dissolved oxygen (DO) is an important indicator of the health of the water and its capacity to support a balanced system of plants and fish.
- Total phosphorus levels are statistically uniform in the lower reaches and upper reaches of all the lakes, except for a weakly significant decrease in the upper reaches of Gravelly Lake. Phosphorus is an essential element for aquatic plant life, but if there is too much it can speed up the aging of a lake.
- Ammonia levels are significantly decreasing in the lower reaches of American, Gravelly, Louise and Steilacoom Lake. Levels are also weakly increasing (marginal significance) in the upper reaches of American Lake, but significantly decreasing in the upper reaches of Louise and Steilacoom Lakes. Too much ammonia is harmful to fish and other aquatic organisms.
- Transparency is slightly trending (marginal significance showing either increasing or decreasing) in American Lake, Gravelly Lake, Steilacoom Lake, Lake Louise and Waughop Lake, and increasing in Carp Lake (although the data set for Carp Lake is small). Transparency measures water clarity – the clearer the water the better.
- The depth of thermal stratification is remaining constant in all lakes. Water temperature changes at the thermal stratification layer in lakes. Denser, colder water is near the bottom of the lake; less dense, warmer water is near the surface. Thermal stratification is most prevalent in the summer months.
The lakes were tested twice a month between May and October from 2000 to 2004. Then in 2005 monitoring decreased to once a month during the same period.