The Great Lake Killer

The great lake killer: algae swells are gross, deadly, and fixable. So why aren’t we doing anything?

YOU KNOW CYANOBACTERIA as blue-green algae and see it in turgid, soupy bloom across Canada. Every summer, excess nitrogen and phosphorus in freshwater bodies suck oxygen from the water, causing roiling dead zones–areas where aquatic plants and animals can’t survive. Simultaneously, this nasty bacteria produces toxins that harms the livers, kidneys, nervous systems and flesh of humans, pets, livestock, wildlife, and fish. It’s now a dominant food source for zooplankton, in turn eaten by many native fish, but as food the bacteria is nutritionally empty–a natural equivalent to junk food. The cascading negative effects run throughout the food web.

North Americans have studied this destructive phenomenon extensively since the 1950s. We know humans have done most of the damage, via runoff from agriculture, septic tanks, wastewater, and commercial fertilizers. And, we know the number of Canadian water bodies contaminated with blooms is rising. Algae swell are a ubiquitous problem in Lake Erie, the shallowest, warmest and most biologically productive of the Great Lakes. Research from Ohio State University in 2013 showed the volume of cyanobacteria per square metre between 2008-2013 was double the volume of the previous six years.


It wasn’t always this way. Blooms decreased significantly in the late 1970s after Canada and the U.S. signed the Great Lakes Water Quality Agreement in 1972. By the early ’90s, algae blooms were rare. Yet cyanobacteria came storming back in the mid-’90s. It’s unclear why, but one theory holds that by consuming cyanobacteria’s competition, invasive zebra mussels allowed their population to explode. True or not, Lake Erie drinking water now often fails to meet World Health Organization standards for safety because of cyanobacteria contamination, leading municipalities to spend an additional $1.2 million annually on water filtration.

This troubling situation isn’t unique to Lake Erie. Lake Winnipeg’s drainage basin (home to three times as much livestock as people) has seen a fivefold increase in blue-green algae between 1969-2003. Lakes experiencing blooms in Quebec rose from 21 in 2004 to 150 in 2009. Seventy-five percent of Alberta’s lakes experience a large-scale algae bloom at least once a year.

This increase in cyanobacteria is mind-boggling. As the climate warms, so much about the future of the Great Lakes–everything from water levels to invasive species spread to the health of aquatic plants and animals–remains uncertain. But cyanobacteria represents an ecological challenge on which we have reams of scientific data, widespread public awareness, and a profound understanding of the issues, and how to curtail them. It’s an embarrassment of riches, but the broader embarrassment is that despite this wealth of knowledge we’ve failed to make cyanobacteria blooms a things of the past.

Frustratingly, a simple solution exists–even if few are using it. In northeast Indiana, a local farmer named Mike Long teamed up with the Nature Conservancy and biologists from nearby Notre Dame University. Their partnership is studying what effect a two-stage ditch has on reducing nutrient-heavy agricultural runoff to local streams–runoff that can, in turn, lead to cyanobacteria blooms. While conventional agricultural ditches drop steeply from either side in a “V” shape, two-stage ditches offer a gradual slope shaped like a stretched “W,” creating a “bench” halfway down the ditch that’s thick with plant life. Compared with a six-foot wide standard ditch, two-stagers hold substantially more water during floods, preventing nitrogen and phosphorous from accumulating in fulsome blooms downstream.

With a foot of snow on the ground, I visited an experimental two-stage ditch in early March. There, I learned that following two years of research on the half-mile trial gully, agricultural nitrates heading to a nearby river were down more than 30 percent; phosphorus levels plummeted 50 percent. Two-stage ditches do this by retaining sediment and fertilizers on the farm, where they’re needed, rather than allowing them to enter local waterways. This can have all sorts of positive long-term effects: What begins life as agricultural fertilizer in Indiana ends up as deadly algae in the Gulf of Mexico a thousand miles away, underscoring that what we do here affects life there. The ecological cliche that everything’s connected is no less important for being true.


While results are promising, two-stage uptake is slow across the Midwest and much of Canada. One estimate suggests just 50 miles of two-stage ditches have been constructed in North America and Europe combined. With the economics ironed out, scaling up two-stage ditches across North America could have huge impacts, as one tool among many, on limiting toxic algae blooms.

Cyanobacteria outbreaks remain a serious environmental challenge we deal with largely when blooms keep us from lounging beachside or when they sicken pets or livestock. We get distressing news coverage in summer months when blooms proliferate before media moves on awaiting what’s now inevitable–subsequent blooms the following year. Yet solutions to these toxic bacterial stews require year-round commitments from individuals, governments, and private interests to implement tested reduction methods while also trying new ideas. Nature employs this design in river valleys to control sediment flow and mitigate flood damage; it’s time we followed suit.

ANDREW REEVES is an award-winning environmental writer, columnist with This Magazine and contributing editor at Alternatives Journal.

Reeves, Andrew