Many lakes including Moses Lake are experiencing increasing levels of blue green algae. Algae growth is driven by nutrients dissolved in the water column. Algae as single celled organisms have no root system as a vascular plant has, and the amount of nutrients, especially phosphorus, have a direct impact on the carrying capacity of the lake to grow algae. In very nutrient rich systems, blue green algae has a competitive advantage because they can fix nitrogen from the atmosphere.
Nutrients come from many sources. They can be present in the inflow water, and as Moses Lake receives water from the Columbia River, the quality of the water moving through the system can be a major factor. There can also be return flow from irrigation delivery systems throughout the Basin upstream from the lake. While septic and runoff from developed areas can also contribute, they are generally not the major contributor to excessive nutrient loading. Lastly lakes are a sink for nutrients, the phosphorus that enters the system can accumulate to the point where internal loading is a significant contributor.
Preventing algae growth is problematic in very large lake systems like Moses Lake. There are a number of algaecides that can provide short term relief, but the Washington Department of Ecology limits these to Hydrothol 191 and Pak 27, a Peroxygen algaecide.
Unfortunately it is not really possible to spot treat algae in areas that are not isolated from the main lake. Algae is windblown and subject to currents, spot treatments kill the algae present in the treatment zone, but it is often back to pretreatment conditions within a day or so as algae migrates back in.
Another limitation is that algae treatments kill and break down the cells, they die back, release the nutrients present in their biomass and that drives additional algae blooms, so even in whole lake treatments relief can be short lived, in some cases only a week or two pass before algae growth fuels back up to problem levels.
Lastly these treatments are extremely expensive for a lake the size of Moses Lake. Moses Lake is 6,800 acres, one application would cost in excess of $1 million USD and this would probably have to be performed more than a few times per summer.
Nutrient management is potentially a better option. Materials like Aluminum Sulfate can be applied to capture phosphorus in the water column. Removing phosphorus removes the carrying capacity to produce algae. One project we have been involved with is outlined in a video at https://www.youtube.com/watch?v=D0iUtkTVGnc and a second project we work on is a reclaimed water reservoir that has had extensive problems for nearby residents for years, one treatment has brought them through the summer.
This is still a potentially very expensive venture given the size of Moses Lake. Our team has collected the information necessary to design and propose a demonstration project in the two isolated bays north of I-90 on Pelican Horn. We will be proposing this to the MLIRD in the next few weeks. This treatment would be performed in the spring and monitored. As results were shown, decisions could be made to move to large areas of focus.
There may also be options to inject and treat the inflow water in future years. The primary problem however may be financial, the size and scope of the operation necessary to clear Moses Lake is driving by the large surface area present. The demo project should help the region make decisions about expanding this approach.