Amid National Water Quality Month, the Oregon Department of Environmental Quality has released the 2017 Survey of Oregon Lakes. The report’s field work component was completed as a part of the U.S. Environmental Protection Agency’s overarching National Aquatic Resource Surveys Program, which includes the National Lakes Assessment every five years. The 2017 Survey of Oregon Lakes provides a statewide evaluation of the ecological condition of lakes and reservoirs. It also represents Oregon’s first-ever assessment of toxic compounds in those water bodies.
Because the sample sizes from Oregon’s earlier NLAs (30 sites in 2007 and 29 sites in 2012) were so small, DEQ was previously unable to make statewide assessments of lake conditions with confidence. However, in 2017, the agency developed a unique survey when it combined funding from the state and EPA to collect samples simultaneously for its Biomonitoring Program, which oversees sampling for the NLA, and its Toxics Monitoring Program. This provided the opportunity to maximize resources and boost the sample size from 29 to 49 randomly selected lakes.
Four additional lakes, or “targeted lakes,” were identified for sampling based on suggestions from DEQ Water Quality staff and the Oregon Lakes Association. They are Lake Abert, Barney Reservoir, Hagg Lake and Woahink Lake. This brings the total of lakes and reservoirs evaluated to 53. The Survey lists the results for the targeted lakes in Appendix A.
DEQ staff collected samples from lakes across the state randomly selected using a probabilistic study design. Each of the sampled lakes was assigned a “weight” representing a certain number of the total lakes in Oregon. For example, smaller lakes are more numerous, so they received larger weights—meaning they represented a greater number of lakes than larger ones. Applying weights to the sampling results allows inferences to be made about all lakes in the population, not just those physically sampled. The sampling results were compared to benchmarks developed by the EPA from ecoregion-specific “reference sites” to evaluate the lake conditions. For the toxics component, sampling results were compared to fixed benchmarks for the compounds with ecological- or health-based risk values.
Key findings from the report include:
- Biological conditions (e.g., zooplankton, benthic macroinvertebrates) were generally good.
- Excess nutrients were observed as the most widespread indicator of poor condition.
- Lakeshore habitat represented the second highest indicator of poor condition.
- All detected E. coli and microcystin concentrations occurred below recreational contact designations.
- Most compounds included in the toxics assessment were found at concentrations below ecological- or human-health based risk values.
The ecological condition of Oregon lakes is largely good. However, there were areas of concern. Eutrophication, which is increased concentrations of phosphorous, nitrogen and other plant nutrients, is of concern nationally. In fact, the leading chemical stressors observed across all scales – Oregon, the Pacific Northwest and nationally – were nutrients and chlorophyll a.
The next iteration of the National Lakes Assessment is underway through DEQ’s Biomonitoring Program. It currently offers the most cost-effective approach to monitoring Oregon’s lakes at the state scale.
By Dan Brown, natural resource specialist, DEQ Laboratory and Environmental Assessment Program