University of Michigan researchers and their partners predict that western Lake Erie will experience a harmful algal bloom of cyanobacteria this summer that is smaller than in 2017, yet larger than the mild bloom in 2016.
Scientists expect this year’s bloom to measure 6 on the severity index but could range between 5 and 7.5. The severity index is based on a bloom’s biomass — the amount of its harmful algae — over a sustained period. The largest blooms, in 2011 and 2015, were 10 and 10.5, respectively. Last year’s bloom had a severity of 8.
The annual Lake Erie harmful algal bloom forecast was released Friday by the National Oceanic and Atmospheric Administration, which funds the research. Officials said that while continued efforts are needed to reduce the size of future harmful algal blooms, Lake Erie residents and visitors will still be able to safely enjoy much of the lake this summer.
The main driver of Lake Erie’s harmful algal blooms is elevated phosphorus from watersheds draining to the lake’s western basin, particularly from the heavily agricultural Maumee River watershed. An estimated 85 percent of the phosphorus entering Lake Erie from the Maumee River comes from agricultural sources.
“Until the phosphorus inputs from agriculture are reduced significantly and consistently so only the mildest blooms occur, the people, ecosystem and economy of this region are being threatened,” said U-M aquatic ecologist Don Scavia, a member of the forecast team.
The size of a harmful algal bloom, or HAB, is not necessarily an indication of its toxicity. The toxins in a large bloom may not be as concentrated as in a smaller bloom.
“NOAA continues to develop tools that provide early warning systems for harmful algal blooms, which help visitors and the community make better informed decisions about recreation activities,” says W. Russell Callender, assistant NOAA administrator for the National Ocean Service. “The resources and services the lake provides drive our economy, and we’ll keep working with our partners to bring the most accurate forecasts for the region.”
In recent years, visible blooms have not appeared until late July or early August. Microcystis, the cyanobacteria that form the bloom, will typically start growing when water temperatures reach 65-70 degrees, usually in mid-June. This year, the western basin warmed almost two weeks earlier than usual, reaching 70 degrees the last week of May, leading to the appearance of a small bloom.
“This early start does not change the forecast severity, because the bloom is determined by the amount of phosphorus that goes into the water,” says NOAA oceanographer Richard Stumpf. “(Paying) close attention to the weekly bulletins will be important through July and August to find the best places to enjoy the lake.”
