ST. JOHNSBURY, Vt. — Vermont officials are trying to adapt to a tougher drinking water standard for a chemical used to fight the sea lamprey, an eel-like creature that has hurt fish populations in Lake Champlain.

Officials with Gov. Peter Shumlin’s and Sen. Patrick Leahy’s offices confirmed Friday that they’ve been negotiating over the use of the anti-lamprey chemical TFM since the state changed its safe drinking water standard from 35 to 3 parts per billion. The move came after the state Health Department questioned the veracity of the 1970s study on which the previous standard was based.

The situation has raised an alarm among fishing enthusiasts worried that scaling back on the use of TFM could cause lamprey to boom and reverse the gains made against the creature, an invasive species that attaches itself to and can hurt the health of salmon, walleye and other species.

“The native and endangered fisheries are sick with sea lamprey,” James Ehlers, executive direct of the fishing and clean-water advocacy group Lake Champlain International, said in a Facebook post Friday.

Mary Borg, deputy director of the state Department of Environmental Conservation’s watershed division, said Friday that the new standard would mean a longer time after application of the chemical during which people would be urged not to drink or swim in affected water.