Ralph I. Lancaster Jr., an attorney with Pierce Atwood of Portland who lives in Falmouth, was appointed a “special master” by the Supreme Court in the longstanding fight between the states over the supply of water in a shared watershed.

A hearing on the lawsuit, filed by Florida against Georgia, is scheduled to begin Monday in federal court in Portland.

The Associated Press reported that arguments are expected to last for weeks, with the outcome possibly affecting millions of people and major industries in both states.

The dispute centers on the Apalachicola-Chattahoochee-Flint River Basin, a watershed that drains nearly 20,000 square miles in western Georgia, eastern Alabama and the Florida Panhandle.

Florida claims that Atlanta and southwest Georgia farmers are using too much water and hurting Florida’s oyster industry. Georgia argues that limiting its water use will harm the state’s economy, the AP reported.

Florida wants the court to impose a cap on Georgia’s water use, with added restrictions during droughts. Their attorneys will argue that Georgia is responsible for lower river flows across the border to Florida. Georgia wants the court to reject Florida’s request for a water use cap.

Lancaster, who could not be reached for comment Sunday, has been appointed a special master by the Supreme Court on four different occasions, according to a profile posted on his law firm’s website.

Lancaster previously served as trial counsel for the United States in a dispute with Canada that was argued before the International Court of Justice at The Hague. He has been ranked by Chambers USA as one of the best lawyers in America since 1983.