A microscopic algae normally found in colder waters has been found in waters of the Delaware Water Gap National Recreation Area and is threatening to suffocate native fauna on streambeds, according to the National Park Service.

Water Gap Superintendent John J. Donahue says extensive mats of the invasive aquatic algae Didymosphenia geminata (also known as didymo or "Rock Snot") were discovered in the Delaware River within the Delaware Water Gap National Recreation Area. An aquatic biologist working for the Delaware River Basin Commission discovered the algae bloom earlier this month.

Currently, the large blooms of didymo in the Delaware have been determined to extend across a 100-mile stretch of river, from an area near the confluence of the East and West Branches of the Delaware near Hancock, New York, downstream to the vicinity of the Dingmans Ferry Bridge.

Additional surveys to determine how far downstream the blooms extend are planned but have been hampered by higher water levels this past week. This known impacted section of river includes portions of two national park units: the Upper Delaware National Scenic and Recreational River and the Middle Delaware National Scenic and Recreational River (within Delaware Water Gap National Recreation Area).

Didymo is native to northern North America and Europe where it prefers waterways with cold water; however, in recent years, its range has expanded to include streams in warmer climates, according to the Park Service. Its branched stalks form strong attachments to the streambed, rocks and aquatic plants and it has the ability to reproduce quickly and form dense mats up to 8 inches thick.

Didymo cells contain silica that gives the algae a rough texture similar to that of wet wool, unlike many other types of algae that feel "slimy" to the touch. It can also be recognized by its brown or tan color and may exhibit long white "tails" that resemble strands of toilet paper. It is unknown at this time why it is spreading so quickly. There is no known method for controlling or eradicating didymo once a water body becomes infested, so containment is critical.

The alga is easily spread through recreational activities and gear. Microscopic spores can hitchhike on boats, clothing, shoes, and fishing gear- even on pets who swim in waters where it is present. Therefore, recreational users of the Delaware River must take precautions to avoid spreading this invasive species into other non-infected waterways in New York, Pennsylvania, and New Jersey.

"The spread of didymo into tributaries could severely impact the ecological balance as well as fishing opportunities in those waters, which in many cases are high and exceptional value trout streams," said Kara Deutsch, Acting Chief of Resource Management and Science at the park.

The dense algal blooms can carpet a streambed, choking out other organisms that live on the stream bottom and thereby reducing the availability of natural food on which trout and other fish species depend. It is critical that anglers who fish both the river and adjacent streams take every precaution to prevent the spread of this invasive species especially at this time of the year when shad and trout fishing are at their peak.

"The National Park Service needs everyone's help to contain this invasive species and prevent it from spreading into other waterways within the park where it will have a detrimental effect on both natural resources and recreational activities. Anglers and boaters can help us stop the spread," said Superintendent Donahue.

Inspect, clean and dry: Didymo can survive outside of the water for over a month in cool, dark and damp conditions. All boats, paddles, propellers, tackle, clothing, and any other gear used within the Delaware River corridor should be cleaned using a detergent and/or bleach solution. After cleaning, items should be dried thoroughly for at least 48 hours before using in another body of water. Felt-soled fishing waders are extremely difficult to thoroughly disinfect as microscopic spores can become imbedded in the felt soles. They are banned in several New England and Mid-Atlantic states impacted by didymo. The National Park Service highly discourages use of felt-soled waders.

National Park Service employees are coordinating with scientists from Pennsylvania, New York, New Jersey, and the DRBC to quickly alert the public and identify appropriate steps to contain this aquatic invader. For more details, including additional information on didymo and how to prevent its spread by properly cleaning equipment before entering another stream or river, please visit:

N.Y. State Dept. of Environmental Conservation at this site, or the Pennnsylvania Fish & Boat Commission at this site.