Each year, the western basin of Lake Erie experiences a Harmful Algal Bloom (HAB) during the summer months. There is a known relationship between the amount of phosphorus (the nutrient that feeds algal growth) that reaches Lake Erie from April-June and the severity of the HAB the following summer. The National Oceanic and Atmospheric Administration (NOAA) releases weekly HAB bulletins from May to October. In the spring, these reports use the total phosphorus load from the Maumee River to predict the severity of the upcoming HAB, and in the summer months, the bulletins provide information on the current and predicted status of the HAB for the following week. NOAA releases a final season summary in late October.

 

On June 20, 2019, NOAA released their final predictive bulletin, and on July 11, 2019, they announced their final prediction for the 2019 HAB season. This year's HAB was predicted to have a severity of 7.5 on a 10-point scale with a possible range between 6 and 9. The severity index is an indication of the total amount of algae (biomass), not the toxicity of the bloom. There is currently no method to predict the toxicity of the HAB. Although there was a lot of rain this spring, the amount of total biologically available phosphorus (TBP) was less than expected based on the known relationship between the river discharge (flow rate) and nutrient load. Some scientists are theorizing that might have had something to do with a necessary, but unplanned change in fertilizer application because of the late 2018 harvest and the amount of spring rain in 2019 that delayed planting, which resulted in less TBP applied and therefore leaving the fields during the critical spring-time window. 

 

NOAA released it's seasonal assessment on October 31, 2019, stating that the 2019 bloom had a severity index of 7.3 (very close to what they predicted!).  This is considered to be a relatively severe bloom (compared to a 3.6 in 2018, but not as bad as 2011 or 2015).  The bloom developed quickly and reached its peak in August with maximum areal coverage of 700 square miles.  Thanks to the high winds in September, the bloom dissipated by early October. Check out NOAA's website for more information or to sign up for their bulletins here.

While the Detroit River itself doesn't experience Harmful Algal Blooms, it is a conduit for phosphorus from its watershed and other sources upstream. The phosphorus delivered by the Detroit River is a contributing factor to HABs in the western basin of Lake Erie and also to hypoxia (low oxygen) in the central basin of Lake Erie. In addition to the HAB in Lake Erie, there was once again a persistent HAB on the southern shores of Lake St.Clair, which impacts recreational beach use and results in extra effort to treat drinking water in parts of Essex County, Ontario. The Thames River in Ontario also experienced a HAB in September, which is only the second time the River itself has had a bloom.