RENO, Nev. — A federal lawsuit accusing the Lake Tahoe Visitors Authority of polluting the alpine lake with debris from Fourth of July and Labor Day fireworks says the tourism agency and its contractor should be subject to up to $75 million in fines.

Joseph and Joan Truxler of Zephyr Cove, Nev., on the lake’s southeast shore, insist their suit is not intended to halt the boat-launched displays that have wowed visitors for three decades.

But they’re frustrated by what they say is the authority’s indifference — and state and U.S. regulators’ failure — to protect the lake from the debris and chemical pollutants.

The lawsuit filed in U.S. District Court in Sacramento in November alleges that thousands of violations of the Clean Water Act were committed over five years.

Judge Troy Nunley agreed last week to extend until Feb. 10 the deadline for the authority and Pyro Spectaculars North Inc. to respond to the suit.

Both are accused of discharging trash, debris, munitions and chemical residues into the lake.