Some of the Island's heavy hitters in shellfish and water quality management are warning MassHighway to slow its plans for the construction of a temporary drawbridge across Lagoon Pond.

On Monday they will travel to Boston to ask officials at the state agency to build time into the project schedule for an environmental study.

Replacement of the existing bridge "doesn't appear to be an emergency and there is plenty of time for the state to take into account the bigger picture - not only the health of the Lagoon, but how the bridge fits into transportation planning for the Island," said Melinda Loberg, president of Tisbury Waterways Inc.

The trip comes a week before a scheduled Nov. 24 public hearing here on the Vineyard, at which Islanders will weigh in on MassHighway's preliminary plans for both a temporary and permanent replacement of the bridge.

As the hearing approaches, Islanders are also pressing for alternative solutions. Talk of a tunnel - an idea first proposed by Tisbury public works director Fred LaPiana - continues.

"This would be a great project, and the conditions are ideal," said Sandy Saunders, a New York-based tunnel consultant who is taking a look at the project. "It's doable, affordable and the beauty, safety and health of the Lagoon would all improve tremendously."

MassHighway manager Steve McLaughlin arranged the Boston meeting after hearing about Islanders' growing concern for the project. A representative from the Coast Guard, which will permit the project once the state files its plans, also will be there.

Among the Island representatives will be Ms. Loberg; Rick Karney, director of the Martha's Vineyard Shellfish Group; Mr. LaPiana, and David Grunden, Oak Bluffs shellfish constable and a member of the Lagoon Pond Association. Selectmen from both Tisbury and Oak Bluffs also have been invited.

"This is less of a political meeting and more about concerned citizens who are focused on environmental issues," said Ms. Loberg. "It is a nice courtesy that the state has asked for this meeting in advance of the public hearing, which will be a wider opportunity for people to have input."

In July MassHighway unveiled preliminary plans to build a $3.8 million temporary drawbridge before beginning construction on a permanent replacement. The plan calls for filling in part of the Oak Bluffs side of the Lagoon to create a base for the bridge footings, which could reduce circulation in the ailing pond.

Poor water quality has been documented in the Lagoon going back as far as 1987, and this July nearly four million healthy juvenile shellfish under culture at the Lagoon Pond hatchery died because of it.

Tisbury Waterways Inc. is now hoping to jump-start a nine-month hydrographic study of the Lagoon. The study will take into account water depth, current speed and size and shape of the pond basin relative to the channel. The information then goes toward building a computerized circulation model that can predict the effect of dredging projects on the pond.

"This is a very important study for the state to have in its possession when it's deciding how to approach the bridge project," said Ms. Loberg. "This way everyone will understand what needs to be done prior to mitigate any environmental impacts."

She added: "This is about information gathering that we feel the state ought to make time for. We don't know enough to make any recommendations or to have a favorite solution yet."

Ms. Loberg said she hopes skepticism about a tunnel does not prevent MassHighway from considering all the alternatives: "It may be one of those fantasies, but let's say what if?"

That's just what Islander Nat Benjamin has done.

The co-owner of Gannon & Benjamin Marine Railway in Vineyard Haven invited Mr. Saunders, a longtime friend, to the Island last week to take a look at the Lagoon. Mr. Saunders owns Saunders Foundry Supply in Cold Spring, N.Y., and has visited tunnel sites around the world, including some in Switzerland and northern Italy, where he said some of the most sophisticated techniques have been developed.

Mr. Saunders said tunneling under the channel between the Lagoon and Tisbury harbor would not pose any significant engineering challenges, and has contacted several major construction companies to ask for their feedback on ballpark cost and feasibility.

"Tunneling gets more challenging the deeper you go," said Mr. Saunders. "But the channel depth going into the Lagoon is fairly modest, so that makes it an easy shot. And the sand is stable without being a hard muck that would make it difficult to [tunnel].

"You could do a rather short tunnel starting on the causeway where the tanks and the warehouses are and coming up just beyond the bridge, or continuing under past the hospital to the 90-degree bend just beyond."

Mr. Saunders said a tunnel of either length would be similar to the underpass of a railroad: "You could have two sidewalks and a bike lane and it wouldn't be a big deal."

He added: "You also could do a tunnel from the Tisbury landfill to the hospital. That would be pretty bold, but there are advantages: The tunnel portals are well above the tide line and any possible storm surge, and you're eliminating any summer traffic snarl in downtown Vineyard Haven. It would be local rather than through traffic."

Mr. Saunders described a machine-bored tunnel as a fairly unobtrusive construction project: "Basically you have a great big rotary digging machine that forces its way along without so much as a rumble on the surface."

Mr. Saunders had no estimate for the project cost.

Mr. Benjamin, a wooden boat builder, was encouraged at the suggestion that a tunnel may be more than a pipe dream:

"They've been closing off the Lagoon for years, just strangling it," he said. "The tunnel would have much less environmental impact - they could even widen the channel. Then you have better access for boats, better circulation. It would be beautiful - not like that eyesore of a bridge. Just a beautiful open space for swimming and recreation."