The intense heat wave that settled over Chesapeake Bay from early to mid-July helped trigger massive fish kills in the Upper Potomac River and Baltimore’s Inner Harbor. Maryland Department of the Environment scientists counted some 21,000 dead sucker fish, catfish, smallmouth bass and others floating along a 14-mile stretch of the river above Great Falls over the Fourth of July weekend. A few days later there were more than 100 dead blue crabs and other fish species floating in the waters of the Inner Harbor and raising a pungent odor.
The scientists said in social media posts the causes weren’t exactly the same—low dissolved oxygen that led to a “Pistachio Tide” in the harbor and drought in the Potomac, along with pollution in both places. But the heat played a significant part.
MDE biologists recorded a record-breaking water temperature of 94 degrees Fahrenheit in the Potomac, much higher than the species that swim in that river can tolerate. And Gussie Maguire, Maryland staff scientist at the Chesapeake Bay Foundation, explained the “Pistachio Tide,” a green sheen on the surface is caused by heat as well…