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Environmentalists report uptick in dead blue crabs, fish in upper Indian River

Center for the Inland Bays

Delaware environmentalists report finding an increased number of dead fish and blue crabs in the upper Indian River this year.

The shallow canals and creeks go through daily cycles where plants and algae release oxygen into the water through photosynthesis during the day and marine animals take in the oxygen at night.

Center for the Inland Bays Science and Restoration Coordinator, Dr. Marianne Walch says high nitrogen and phosphorus levels in the water fuel algae blooms of phytoplankton called gyrodinium. The excess algae, she says, creates an imbalanced oxygen cycle.

“You can see the oxygen go down to almost zero at night by the time the sun comes up in the morning around six a.m. and the levels of oxygen that occur at night are typically very unhealthy for the fish and the other creatures in the bay,” said Walch.

This change kills a number of menhaden in the upper Indian River each summer—in part because of long days, warm water and lots of sunlight.

Walch says this year those numbers are up and people are spotting dead blue crabs as well.

“We’re not completely certain why the crabs are different this year, but we are fairly convinced that the problem we’re seeing in the Indian River is due to nutrient pollution,” said Walch.

Walch points to area agriculture, stormwater runoff and Mountaire’s treated spray irrigation system as causes for the high nutrient levels.

She says crab carcasses have been sent to labs for analysis and continuous monitoring sensors have installed in the Indian River to keep detailed track of nutrient, oxygen and pH levels.

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