Susan Dangel with the citizens group Save Mashpee Wakeby Pond Alliance screened recent aerial footage of Mashpee River and Shoestring Bay at this week’s Mashpee select board meeting.

The video shows large amounts of green algae overtaking sections of those areas.

Nitrogen from outdated septic systems has led to the degrading health of those waters, and Dangel called on the board to act.

“I can’t imagine what’s going to happen when people show up next week to rent one of those properties,” she told the board. “They’re never coming back.”

Andrew Gottlieb, Executive Director of the Association to Preserve Cape Cod, also spoke at the meeting.

Referencing the video, he said, waters won’t improve without action.

“What you saw is disgusting, and it’s going to get worse. It’s going to get worse this year. It’s going to get worse next year. And it’s going to get worse until enough nitrogen starts coming out of the ground.”

Gottlieb recommended the town move up its timeline to finalize the next phase of sewer work to meet an important deadline for state funding this summer.

Future work could be held up for a year if that deadline passes.

The discussion in Mashpee comes as towns across the Cape are taking on extensive sewer projects to improve water quality.