As guardians of a special lake of superior clarity, homeowners around Christmas Lake are pondering a serious question: Should they dose the entire body of water with chemicals to kill off Eurasian water milfoil?

Up to now, they have battled the invasive weeds on the west metro lake with a mechanical harvester that has the effect of a water lawnmower. Some individuals also have applied herbicide on a spot basis in front of their homes.

But after a messy, poorly done harvest last summer that left some shoreline littered with milfoil, some members of the Christmas Lake Homeowners Association felt they were losing the battle and stopped paying dues.

The green, feathery underwater plant is a problem for Christmas Lake and hundreds of other lakes across the state because it grows so thickly it gets in the way of boating and swimming and crowds out native plants that keep water clear and provide habitat for fish.

On Thursday night, about 30 of the 142 Christmas Lake homeowners gathered at Excelsior Elementary School to discuss options for the coming summer and hear more about a chemical called fluridone.

It is a whole-lake herbicide that if applied correctly can kill milfoil but not affect native plants.

Retired federal Judge Miles Lord, a homeowner on the lake and a member of the association board, had sent a letter urging neighbors to turn out to oppose “poisoning’’ of the lake.

With two members from the Department of Natural Resources (DNR) and three lake consultants offering information, residents of the lake — which straddles the Shorewood-Chanhassen border — expressed skepticism and concern about using the chemical.

“I am sitting here as a homeowner who believes I have a responsibility to leave this place better than I got it,’’ said Joe Shneider, of Chanhassen. He said talk of using chemicals scares him because the long-term effects aren’t known.

Others said they didn’t want to make a mistake that would hurt the lake’s water quality.

The lake is especially clear because it is spring fed with a sandy bottom and has a small watershed for surface runoff. It has 25 varieties of native plants, compared with five to 10 for most metro lakes. Milfoil was discovered there in 1992. Since 1999 or 2000, the association has spent about $20,000 a year to cut the weeds twice a summer.

But the milfoil has seemed to grow worse, and frustration from homeowners propelled association President Harley Feldman to discuss the chemical with the DNR.

The DNR staked out a careful position, saying it would not go so far as to recommend whole-lake treatment with fluridone but would permit it if a majority of homeowners supports it. The chemical would have to be applied every three years.

The DNR has tried fluridone seven or eight times around the state and still considers it experimental, the DNR’s milfoil expert, Charles (Chip) Welling, told the group. Welling said whole-lake treatment is complicated and has to be monitored carefully because “if something goes wrong, it goes wrong lakewide.’’

Two consultants who advised the homeowners on the milfoil have a split opinion on whether the whole-lake treatment is right for Christmas Lake.

Dick Osgood, a national lake management consultant who is also the executive director of the Lake Minnetonka Association, told the audience that there is no evidence to support concerns about fluridone.

In an interview Friday, Osgood said the U.S. Environmental Protection Agency has tested fluridone thoroughly and found it safe. The concern is that it be applied properly, Osgood said. “The benefit of fluridone is that it can target milfoil and leave native plants unharmed or minimally harmed. But if you misapply it, there can be unintended effects.’’

Experience has improved the reliability, Osgood said. “Michigan has used this product on over 300 lakes, and their DNR has not reported a single incident of this going wrong.’’

But Steve McComas, a lake management consultant with Blue Water Science of St. Paul, said in an interview Friday that “Christmas Lake is such a remarkable lake’’ that he recommends harvesting over the chemical treatment to avoid any risk of degrading water quality. “If this was almost any other lake, I would say the risk is worth it. But Christmas Lake is one in 1,000,’’ he said.

Hired by the Christmas Lake association to survey the plants in the lake, McComas put a rake in the water and pulled out what was growing at more than 100 locations on Christmas Lake. He added 2007 data to similar surveys he had taken several times since 2001. The results show milfoil is increasing and native plants are decreasing.

But McComas noted that while native plants are decreasing in distribution, the overall number of plant species is staying the same or increasing. “So there is a mixed message there.’’

McComas, who said he wasn’t asked to give a recommendation at the meeting, listed three good options: “Doing nothing, herbicides or harvesting. Of those, harvesting is the safest. That removes the surface canopy, removes the biomass of excessive growth and should allow native plants freedom to grow.’’

He advised the association to “get a better harvesting company and set some priorities. I would go with something that is not as good as whole-lake chemical treatment but has a lower risk.’’

The next step, said Feldman, is to survey homeowners for their opinions on the options.

Laurie Blake • 612-673-1711