A river system in hot water

August 13, 2007

AFTER BLOOMS of toxic blue-green algae appeared in the Charles River recently, environmentalists began calling for a reduction in the hot water that a Cambridge power plant discharges into the river. A spokeswoman for the Mirant-Kendall plant says it is not to blame; the discharges, she notes, have occurred in years without algae blooms.

But even if the plant's hot water discharges on their own weren't enough to cause algae growth in the past, they are demonstrably a factor in recent blooms and are clearly harmful to the river ecosystem. Mirant-Kendall's request to renew its permit for heated-water discharges is now before the appeals board of the US Environmental Protection Agency. The panel should move quickly to impose strict limits on the discharges -- especially in spring months, when fish are spawning, and during the summer.

Usually the biggest impact from power plants on the environment is air pollution. But a plant like Mirant-Kendall, which uses water for cooling, compromises that water source in two ways. First, it sucks in millions of gallons a day, destroying fish, eggs, and larvae in the process. Second, it discharges water at warm temperatures -- up to a bath-like 105 degrees in the summertime. Heated water, high phosphorus levels, and sunlight provide an ideal habitat for algae blooms.

The blue-green substance is actually a form of bacteria, Cyanobacteria. Its cells include a toxin that is released when the cells die, so the danger persists even when the bacteria are no longer visible. While the toxin can cause a skin rash and irritate the nose, eyes, or throat, it is most harmful to people when it is ingested, and can lead to liver and nervous system damage. Kate Bowditch of the Charles River Watershed Association worries in particular about dogs; they seem to find Cyanobacteria water especially enticing, she said. She has not yet heard of dogs made sick by Charles River water, she said, but there have been cases elsewhere.

When the EPA appeals board weighs the plant's permit, it is required to consider that the Charles has important recreational uses, including boating and windsurfing, and is on track to become swimmable. This summer, a demonstration swim on the river came close to being canceled because of Cyanobacteria.

The Mirant-Kendall discharges are just one of the problems the Charles faces. Its quality is also harmed by bird and pet waste, combined water-sewer overflows during storms, runoffs from nutrient-rich fertilized lawns, and other pollutants. The Cyanobacteria is a blue-green canary in a mine that deserves even more attention than it has gotten, despite years of improvements upstream. A strict limit on power-plant discharges of heated water is a step in achieving the Charles's potential as a resource for both marine life and human recreation.