Under the Great Lakes Water Quality Agreement, the U.S. and Canada, with the Lake Erie states and province, have agreed to work together to reduce the amount of phosphorus entering the western and central basins of Lake Erie by 40 percent (from 2008 levels). ErieStat will track progress toward this goal and support the Annex 4, Nutrients, Subcommittee convened under the Water Quality Agreement. The governments of Michigan, Ohio, and Ontario have further agreed to achieve the reductions for the western basin by the year 2025 with an aspirational goal of a twenty percent reduction by 2020.

Download the ErieStat fact sheet here.

Tracking Progress

Total and soluble reactive phosphorus (SRP) are tracked in the spring period of March-July to measure progress at eight priority tributary watersheds identified as contributors to harmful algal blooms in the western basin.

  • ErieStat presents information as both loads (the total amount of phosphorus entering the lake from a tributary) and flow weighted mean concentration (FWMC) – which standardizes the measure of phosphorus delivery from a tributary so that performance can be compared across years and tributaries despite different flows.

  • For example, in a dry year the load may be low due to less runoff, but the FWMC will still be high if the phosphorus concentration in that runoff is high.

graph of spring SRP loading and spring discharge - maumee river

Modeling suggests that annual total phosphorus loads influence the extent and intensity of hypoxia (low oxygen) in the central basin.

  • Limiting the annual total phosphorus load is thought to raise the oxygen concentrations in the bottom waters of Lake Erie to an acceptable level.
  • The annual total phosphorus load is tracked at ten priority tributaries and also estimated for the entire western and central basin. 
graph showing provisional Total P Loading Estimates