Concerned, Uhlman paddled her kayak into the pond to see how far the algae had spread.

“I kayaked around and I was leaving a trail — you could see where the kayak had cut through the slime,” she said. “You feel almost scared, like, ‘What is going on?’ And that it’s never going to clear up and that the pond is dying.”

Uhlman’s pond did clear up that fall, but algal blooms are an ongoing problem on the Cape. Even the more common, nontoxic growths are destructive, creating low-oxygen dead zones that kill fish and native plants. Now, 90% of Cape Cod’s coastal bays and more than a third of its ponds have “unacceptable” water quality, according to the nonprofit Association to Preserve Cape Cod’s annual State of the Waters report.

“We’ve seen a significant deterioration of our bays to the point where they’re designated as impaired, where we don’t have shellfish, we don’t have finfish,” said Barnstable town manager Mark Ells.

The pollution comes primarily from septic systems, which leach nitrogen and phosphorus — basically fertilizer — in the Cape’s groundwater. The state has tough new regulations that are forcing communities on the Cape to clean up the water. And towns are now grappling with the cleanup’s enormous price tag: in Barnstable alone, cleanup will cost more than a billion dollars.

It’s a critical moment for Cape Cod. The Cape has more than 550 miles of coastline, at least 890 freshwater ponds and 53 small saltwater bays bordering the ocean. That water is the Cape’s raison d’être: residents and visitors use it for swimming, boating and fishing, and it forms the backbone of the region’s $1.4 billion tourism industry. Now Cape Cod communities are scrambling for solutions before their ecosystems, economies and property values collapse.

“Most of our own personal financial wellbeing is intimately tied to the Cape continuing to be an attractive place to live. And so, as individuals we’re all at an enormous risk,” said Andrew Gottlieb, executive director of the Association to Preserve Cape Cod.

“People like Cape Cod and want to come to Cape Cod, and to a certain extent, they’re loving it to death…”