Hancock’s Norway Pond Commission is working with the New Hampshire Department of Environmental Services to address water quality issues at the 20-foot-deep Norway Pond.
NHDES Chief Aquatic Biologist Amy Smagula said the pond is experiencing internal loading — a process in which sediment releases nutrients like phosphorus and nitrogen into the water, fueling algae and bacteria growth.
Runoff carrying fertilized soil contributes to the problem, she said, as nutrients settle to the bottom and are later released when oxygen levels drop, creating a condition called anoxia.
“Anoxia causes the sediment to release the nutrients promoting growth of algae and cyanobacteria,” Smagula said. Cyanobacteria, a type of phytoplankton, can produce toxins harmful to people, animals and the environment.
To combat the issue, NHDES recommended increasing vegetation along the shoreline, noting that grassy areas currently dominate much of the pond’s edge.
“Grass roots don’t infiltrate the soil well, so heavy rain washes out areas of soil without deep root systems,” Smagula said, adding that planting trees and other vegetation with deeper root systems would create a buffer to filter nutrients from runoff.
She also proposed expanded water monitoring, including installing a sensor to track oxygen levels over five months and conducting regular sampling from May through September.
She said that data from preliminary sampling by the state shows oxygen levels decline between June and August, but Smagula said more detailed sampling — including phosphorus and plankton collection at the inlet, outlet and different depths — would help determine where and when cyanobacteria is forming.
“By gathering plankton and phosphorus from these areas, we can see how much is coming from each and compare them,” she said. “If we don’t find that the cyanobacteria is forming at depth, then it may be forming along the shore.”
The data will help guide future mitigation efforts to improve water quality in the pond. Smagula said phosphorus sampling will cost about $500.