State officials say an invasive aquatic algae that turned up last summer in the Connecticut and White rivers and the Batten Kill has now been spotted in the Mad River, its first incursion into the Lake Champlain basin.
Water quality scientists for the state have confirmed the presence of didymo in an area of the river near Warren.
The algae, which tends to thrive in cold, clean waters and low-nutrient rivers, threatens aquatic insect and fish populations. It has contaminated rivers in Arkansas and Tennessee but until last year hadn’t been seen in the northeastern United States.
Didymo is spread by boats, gear and fishing equipment, adhering to them and then moving as the equipment is used in other bodies of water.
Spotted first by a citizen, the algae is coating rocks and may have already spread to other parts of the Mad River.