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Heat wave likely killed Assabet River fish

Posted by John Swinconeck  July 26, 2013 01:33 PM

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OARS, a non-profit group that monitors and protects the Assabet River, is blaming the recent heat wave for hundreds of dead fish found floating in the river on July 20.

OARS volunteers removing an invasive plant species “discovered the floating remains of hundreds, if not thousands, of fish in the Assabet River in Stow,” the group said in a statement.

So-called fish kills can occur because of pollutants, and also by high water temperature and a lack of oxygen in the water.

“After two days of much cooler weather (on July 22nd) we measured afternoon water temperatures still over 86°F in the area downstream of the fish kill," said OARS scientist Sue Flint. "Where the river is shallow and slow-moving, afternoon water temperatures can reach lethal conditions--93°F is lethal for almost all species of fish.”

If fish have no deep or shaded places to retreat from the heat fish kills like this occur. Narrower sections of the river are lined with trees that provide shade. Groundwater also contributes cool springs that provide a safe haven for fish during heat waves.

According to OARS, evidence of changing rainfall patterns and temperature tells us that these problems are going to become worse rather than better unless major efforts are made to improve the resilience of the region's rivers and streams. Last year was the hottest year in Massachusetts out of a 118-year record.

Over the past 64 years the intensity of rainfall has increased dramatically in New England, resulting in more floods but also less recharge of the cool and clean groundwater that feeds the rivers in the summer, OARS said.

“There are many things communities can do to improve the resilience of their rivers and streams,” said OARS Executive Director Alison Field-Juma in a statement. “Recharging stormwater into the ground will make a big difference, and reducing nutrient pollution through decentralized wastewater treatment with ground discharges will also help. This requires longer-term investment than we are used to making. Protecting floodplains and riverbanks from development is as important as ever.”

Those who wish to report a fish kill should contact OARS at (978) 369-3956 or office@oars3rivers.org, and to MassWildlife at (508) 450-5869.

Contact John Swinconeck at johnswinc@gmail.com. Follow @johnswinc on Twitter.

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