The Maine Department of Environmental Protection began herbicide treatments to kill the invasive plant hydrilla in Damariscotta Lake on June 25.
The DEP is using the chemical fluridone in minute amounts to target the species, which many officials refer to as “the worst of the worst.”
A Damariscotta-Lake-Watershed-Association-trained volunteer identified hydrilla in Damariscotta Lake last fall, and the DEP began work containing it immediately.
“We pulled out several tons of plants by hand,” said Paul Gregory, with the DEP invasive species program. “It was so dense that it was like bales of wet hay.”
Hydrilla’s roots contain tubers that can live underground for as long as 12 years and can grow into new plants at any time, so it’s almost impossible to remove by hand, Gregory said.
The hydrilla population in Damariscotta Lake appears to be several years old and has a healthy tuber population, Gregory said.
Fortunately, the plant appears to be largely contained to a .3-acre lagoon near a part of the lake known as the Narrows. A few plants have been found outside the lagoon, but no large infestations have been discovered in other parts of the lake at this time.
The lagoon has been sealed off with riprap and plastic screens, and the lagoon has now been treated with herbicide.
Herbicide is usually a last resort, Gregory said. “In this case, we thought we should be as thorough as possible.”
At an informational session about the herbicide treatment on May 27, several residents raised concerns about the environmental ramifications of using a chemical treatment in the lake.
The herbicide was carefully applied in extremely small doses, Gregory said. The herbicide should remain contained to the lagoon, and at the levels at which it is being used in Damariscotta Lake, it will not affect any animal species, Gregory said.
In order to kill hydrilla, fluridone must be applied at a level of 6 to 10 parts per billion, the level at which it has been applied in Damariscotta Lake.
In other words, there is 6 to 10 milliliters of herbicide in every 1 billion milliliters of water in the lagoon in Damariscotta Lake.
Fluridone does not affect fish until it reaches a level of 4 million to 7 million parts per billion, Gregory said.
According to Environmental Protection Agency regulations, Fluridone can be used in public drinking water supplies at levels up to 150 parts per billion.
Now that the area has been treated, the DEP will monitor the water both inside and outside the lagoon to make sure that herbicide levels remain in the effective range. Sunlight breaks down fluridone, so it will need to be reapplied at least once this fall, Gregory said.
In late September or early October, the herbicide will likely be gone and the DEP will put down benthic barriers – tarps that cover the bottom of the lake to prevent plants from growing, Gregory said.
“The barriers are the long-term strategy,” Gregory said.
In the future, the barriers will either be removed to allow native plants to return to the lagoon, or they will be left down and silt will be allowed to collect on top of them, creating a new layer of bottom for native plants to grow, with the hydrilla trapped underneath the buried benthic barrier, Gregory said.
For now, the DEP is cautiously optimistic about the future for Damariscotta Lake and their ability to contain hydrilla, but work on the infestation is far from over, Gregory said.
“It’s good science and it’s being fair to the public to say that hydrilla will likely be a problem in Damariscotta Lake for the long term,” Gregory said. “Eradication is not a work that rolls off the tongue.”
The containment and removal program that the DEP is planning is extensive, but relatively benign compared with what some other states are facing, Gregory said.
Florida spends about $20 million each year mowing the hydrilla in their waterways to make them navigable.
“In California, when they find it in a small lake or waterway, they pave it over,” Gregory said.
Before the DEP will know the extent of the problem in Damariscotta Lake, the rest of lake must be surveyed for infestations. The DLWA is currently organizing volunteers to conduct those surveys later this summer, said Julia Davis, who is coordinating the DLWA volunteers.
About 30 people showed up for their first training session earlier in June, and 33 people have signed up for a session on July 10. That training is full, but space is still available for several training sessions later this summer.
There will be a training session from 2 – 4 p.m. on July 25 at the DLWA headquarters at 38 Lake Farm Rd. in Jefferson for volunteers who want to participate in the lake-wide survey effort.
There will also be a more in-depth training from 2:30 – 8:30 p.m. on July 15 at the DLWA headquarters.
Slots are still open for both sessions, and there will be more training sessions scheduled for later in the summer. For more information or to register for a training session, call Julia Davis at 549-3836.
So far, the DLWA is excited about the response they’ve received to their call for help, Davis said.
“It’s really remarkable how many people have come forward to help,” Davis said.