Lake Michigan Warming: Climate Threats

Graphic showing Lake Michigan temperaure changes You don’t expect to see 75- or even 80-degree water in the Great Lakes in early July or, in most years, anytime. But an exceptionally hot weather pattern has pushed water temperatures in most of the lakes to the highest levels on record so early in the summer. Over lakes Erie and Ontario, the water is the warmest it has been since records began being kept, and could warm more in the coming weeks.

The abnormally warm waters, consistent with climate-change trends in recent decades, could compromise water quality and harm marine life in some areas.

These water temperatures over the Lakes are some 6 to 11 degrees warmer than normal.

Lake Michigan’s average water temperature reached 75.1 degrees on July 8, nearly 11 degrees above normal, and the warmest mark on record so early in the year. The water temperature in July has only been this warm one other time, at the end of the month in 1999.

Lake Michigan’s average water temperature on July 8 was 11 degrees above normal, and the warmest mark on record so early in the year.

Impacts From Rising Water Temperatures

Algae Blooms

National Oceanic and Atmospheric Administration (NOAA) aircraft have already photographed 'blue-green algae' or 'cyanobacteria' over western waters of Lake Erie in recent days. The foul-smelling algal blooms can harm fish and make people who are exposed to the water sick. In 2014, cyanobacteria from Lake Erie entered the water supply in Toledo, and residents were ordered not to drink or touch the water.

The jump-start to the algal bloom due to the warm water temperatures means it will be around for several weeks longer than normal. NOAA stated that this was the second earliest that they have seen algae since 2002

Game Fish

Chinook salmon jumping Many fish do not do well in water that is too warm, so they get ‘squeezed’ into a smaller and smaller area between surface water that is too warm, and bottom water that doesn’t have enough oxygen

The warming is expected to reduce the amount of time cold water fish spend in the southern basin of Lake Michigan, where the chance of catching these species is already limited because it’s shallower and more tepid than the rest of the lake.

Much of the lake is so deep and cold in open water that most fish can’t survive there, but warming will likely open up more habitat for the majority of fish. Whether they will be able to find sufficient food in those new waters is unclear.

This could become a significant problem for some game fish, like trout and salmon, that depend on cold, oxygen-rich waters. However, milder water temperatures are expected to expand the range of warm water fish like bass, which are confined to southern Lake Michigan.

To withstand warmer temperatures, cold water fish, like chinook salmon, will expend more energy and require more food.

Invasive mussel species have decimated the abundance of 'plankton', small organisms that serve as base of the food chain and the staple of many small fish diets.

Invasive mussels have also contributed to the decline of the chinook salmon’s primary prey, a small fish known as the 'alewife', whose population has crashed in the past several decades.

Lake Ecology

Beach Closed Sign Warming temperatures has already increased bacteria levels in the Lake Michigan, as the water warms earlier in the spring and warming contributes to vertical mixing that changes lake ecosystems. Sewer overflows, the dumping of ship ballast water, and nutrient runoff from agriculture and industry all contribute to growth of bacteria and several invasive species in the lakes.

It’s become common in recent years for beaches in Chicago and Michigan to close or be under swim advisories because of bacterial contamination. Beach closures are expected to increase as heavy precipitation exacerbates issues associated with runoff and pushes up bacterial counts as well as algal blooms and E. coli alerts

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