The Lake Erie dead zone returned in 2020 and has grown about 50% larger this year to just over 3,400 square kilometers – one of the largest on record that’s occurred so far in July, says Mike McKay, lead scientist and project manager with Environment and Climate Change Canada.

Researchers with DFO will be out again this year from June to October conducting monitoring that aims to determine not only how large the hypoxic zone or ‘dead zone’ has become, but will try to figure out why one materialized again so soon after 2019 produced little hypoxia over eastern basin bottom waters.

Hypoxia – low oxygen levels that are too low to support aquatic life - in the central basin can affect fisheries (the lake perch’s optimal oxygen levels run around eight milligrams per litre, says Depew), impact fish breeding habitat, change food-web dynamics (zooplankton can get trapped because they prefer warmer less-oxygenated waters close to the surface while feeding at depth) and alter ecosystem dynamics.