Laura Meyerson, a University of Rhode Island ecology professor, compares a native phragmites with a much larger invasive variety on Block Island. A state study found 79 percent of the state’s freshwater bodies have been fouled by at least one invasive species of plants or animals.

The Providence Journal / Andrew Dickerman

Residents living on the Smith and Sayles Reservoir in Glocester can’t go on the water without their boats, kayaks and Jet Skis getting tangled in variable milfoil, a dense, bushy underwater plant that has taken over in the past two years.

The plant has grown so thick that parents are afraid to let their children swim in the reservoir for fear they might get tangled in the weed and drown.

In 2006, the Rhode Island Country Club in Barrington spent $6 million on dredging and reconstruction largely to remove the stands of another invasive species, the reed phragmites. The dredging of Mussachuck Creek increased tidal flow to the wetlands, restricting the growth of the insidious reed, which can survive only in fresh and brackish waters. Milfoil and phragmites are just two invasive species that have taken hold in Rhode Island and elsewhere.

Nationally, a congressional subcommittee on the environment called the country’s invasive species situation “ecological roulette,” because of the economic and environmental damage caused by the invasive species that have taken hold — just a small fraction of those introduced in the country.

And a recent survey by the state Department of Environmental Management found 79 percent of the state’s freshwater bodies have been fouled by at least one invasive species — foreign plants or animals that grow aggressively and seldom have natural predators.

“This was just a survey to find out the distribution of invasive species, said Katie DeGoosh, a freshwater biologist at the DEM, “and they are everywhere.”

Although the data is not comprehensive, it clearly illustrates an increasing problem: more and more invasive species are arriving in state waters.

It doesn’t take much to bring an invasive species to Rhode Island. A boater leaves a piece of dangling plant on his motor. A child releases an unwanted pet into his backyard pond. A prickly seed adheres to a bird’s leg.

But what ensues can be draconian — native species left struggling to survive, environmental damage and significantly reduced value to boaters, swimmers and fishermen.

The rate at which problematic foreign species survive in local waters means an innumerable amount of plants and animals are traveling great distances and finding new ecosystems to host them, said David Gregg, executive director of Rhode Island Natural History Survey.

“If they can be able to become established with this frequency, there are a lot of these things being moved around,” Gregg said. “That is kind of scary.”

LAURA MEYERSON, an ecology professor at the University of Rhode Island, took a recent research trip to Block Island to see whether an invasive subspecies she is studying — the reed phragmites — has hybridized with a native variety.

Meyerson and URI graduate student Kimberly Lellis trudged into marshy ponds where native and invasive stands of phragmites grow side by side.

Meyerson says that even though invasives are becoming an increasing nuisance in the state, not all exotic organisms that are introduced establish themselves. And even fewer become a problem. She calls it the “tens rule”: 1 in 10 becomes established, then 1 in 10 of those becomes invasive, or a problem.

“You leave all its predators, pathogens and parasites behind,” Meyerson said.

Meyerson and Lellis cut and bag samples of both. The invasive stands are noticeably taller and bear fuller feathery seed heads. Concerned about the emergence of “Frankenphrag,” as Meyerson calls the possible hybrid, she will run genetic analysis on the plants in her lab.

“It’s like marrying your cousin,” she said, “you worry about the baby.”

The worry is that if a hybrid has formed it would create a more aggressive species of phragmites.

ENVIRONMENTAL MANAGERS usually find out about new invasions through discoveries by fishermen or high school students working on a science project, Gregg said.

The water chestnut — not to be confused with the tuber popular in Asian food — was only recently spotted in Rhode Island. On Oct. 16, a University of Rhode Island graduate student found a patch of several hundred plants about 50 feet wide in Upper Belleville Pond in North Kingstown.

The plant grows voraciously, choking off native plants and animals and preventing recreational use. “The seeds themselves are wickedly barbed,” said Gregg. “[They] can make it impossible to walk or wade in the pond.”

Early discovery of the water chestnut means the state has a better chance of preventing its destructive spread throughout the state. The Rhode Island Natural History Survey said the state can control the plant’s destructive spread to other bodies of water by pulling it out during the summer before it seeds again. If allowed to spread, water chestnut could become an expensive nuisance. New York and Vermont spend more than a half-million dollars a year fighting the plant in Lake Champlain.

“Assuming we don’t find another pond nearby that is choked with this stuff we are really lucky,” Gregg said. “There are places where ponds are covered from shore to shore.”

Two other invasive species, the zebra mussel and the Chinese mitten crab, have yet to show up in Rhode Island. But officials feel it is only a matter of time.

Both would likely be a nuisance.

Zebra mussels, a freshwater shellfish found as close as the Hudson River, have long been the bane of the Great Lakes since arriving in 1988, clogging water intake pipes and diverting food from native organisms.

Considered a delicacy in Chinese cuisine, the hairy-clawed mitten crab is believed to have been introduced in 1985 on the West Coast through ballast water discharge or intentional importation.

The crab is catadromous, meaning it lives in freshwater and moves to salt water to breed. It burrows into banks, which can lead to increased sedimentation and erosion, and it preys on a variety of fish, mollusks, plants and invertebrates.

So far it has been spotted as close as the Hudson River and Chesapeake Bay.

“I think the Chinese mitten crab would be a big deal here,” Gregg said. “It’s going to have ecological effects and psychological effects. We’re not used to having crabs in our ponds.”

WHILE DETECTION of invasive species has improved, state environmental managers are able to do little to stop them.

Without money to continuously monitor lakes, rivers and ponds and deploy a rapid response, new invaders from other states and abroad will continue to stream into Rhode Island waters, experts say.

Some states, including Vermont, New Hampshire and Maine, have taken steps at prevention with ramp stewards who check boats before they are allowed into the water. But in Rhode Island, no such prevention exists.

“If someone from Maine brought it our way, it would just go right into the water,” Gregg said.

The Coastal Resources Management Council recently submitted an ambitious management plan to the federal government to get money to address the problem. With preliminary approval, it appears Rhode Island will get $50,000 from the U.S. government. The money will be used to educate the public and improve communication with other states and agencies that monitor invasive species, said coastal council spokeswoman Laura Ricketson-Dwyer.

The council has jurisdiction over freshwater bodies within 50 feet of the coast and shares duties with the DEM when waterways flow through both of their management areas. The agency wants to model its invasive-species management strategy after Massachusetts, Ricketson-Dwyer said, enlisting the help of volunteers to inspect boats and spread information.

“On the scale of things, it’s just not a lot of money,” Gregg said. “I think the biggest benefit that we can derive from $50,000 is better communication.”

The DEM is also hoping that spreading the word will help fight invasives.

The same parties who enjoy the state’s freshwater bodies — boaters, fishermen, swimmers and animals — are commonly the modes of transportation that introduce an invasive species to those ponds, streams and lakes. So the department is turning to the public for help.

Starting this spring, the agency will post signs at freshwater public access points instructing those entering and leaving the water to thoroughly clean their boats, boots, waders and gear.

The sign contains illustrations of nine invasive plants and animals, including variable and Eurasian milfoil, fanwort, goldfish, carp, koi, Asian clam, zebra mussels and the Chinese mitten crab.

“Although aquatic invasive species can spread by several different vectors, human behavior is the one thing we can change,” DeGoosh said. “We can’t change bird migrations or wind patterns.”

To learn more about the identification and prevention of invasive species, URI’s College of the Environment and Life Sciences Outreach Center, with the Coastal Resources Management Council, is offering a course on invasive plant management at URI’s Bay campus in Narragansett. The two-day course will be held Jan. 23 and 24 from 9 a.m. to 4:30 p.m. Cost: $150. For more information, call the Outreach Center at (401) 874-4096.

For more information on Rhode Island invasive species, visit the Rhode Island Natural History Survey Web site at www.uri.edu/ce/rinhs/index.htm.

ngarcia@projo.com