East Hampton scientist warns of rising algal blooms, nitrogen and a new toxin in ponds

Dr. Chris Gobler presented a year of water‑quality monitoring to the East Hampton trustees on March 9, saying summer 2025 showed near‑record chlorophyll and several harmful algal bloom events across local bays and ponds.

"We all know why we're here and that's to protect the waters of East Hampton," Dr. Chris Gobler said, summarizing results from more than two dozen sites sampled April through September 2025. He said a sustained alexandrium bloom in 3 Mile Harbor persisted at potentially shellfish‑toxic levels for nearly three weeks, and a Deinophyseus bloom in June–July reached the highest levels his lab has recorded.

Gobler said daytime oxygen readings can be misleading because sensors show large night‑time oxygen drops that can slow or stunt shellfish growth. "When you've had these nighttime drops in oxygen ... shellfish growth rates drop dramatically," he said, noting measured declines of up to 100–200 percent in some cases.

The lab also measured nutrients and indicator bacteria. Gobler said about half of monitored sites exceeded the Peconic Estuary Program nitrogen target that supports seagrass, and several stations registered coliform and enterococcus exceedances on discrete dates in 2025. He cautioned that some high bacteria readings may reflect animal sources, but said additional microbial source tracking will become more informative now that his team has refined primers to separate human, dog and small‑mammal signals.

Wayne Scott Pond drew detailed attention: Gobler reported that the pond has become shallower over seven years, has very high organic‑matter sediment in places, and recorded a detectable level of anatoxin‑a, a cyanobacterial neurotoxin. "This is a system that in a short period of time has really transformed, for the worst," he said.

As a potential remediation, Gobler described work with an engineer and a Massachusetts firm to propose a permeable reactive barrier (PRB) on the pond's northern extent to intercept high‑nitrogen groundwater. He said the town has permitted preliminary field work and that trustees could consider the proposal for funding and permitting.

Trustees asked about irrigation and other upland drivers of freshwater runoff and salinity changes; Gobler said those factors likely contribute but require additional targeted study. He recommended continued biological and water‑quality monitoring to pair any management actions with measured outcomes.

The trustees did not take formal action on the presentation but discussed follow‑ups, including further analysis of groundwater flow and coordination on proposed PRB siting.