FREEPORT – Despite a few trouble spots, the water quality in Casco Bay is generally good, a new analysis has concluded.

Among the problem areas where pollution has lowered oxygen levels to the point where marine life may be affected were built-up sections of Portland Harbor, including Custom House Wharf and Stroudwater Bridge.

Similar problems were detected, surprisingly enough, at the more remote Dyer’s Cove and Ben Island in Quahog Bay in Harpswell.

“We think it might be natural,” said Joe Payne, the baykeeper for Casco Bay. “I hesitate to say that because it’s not without human influences, but it’s more natural in cause than Portland Harbor.”

The findings were presented Wednesday at “The State of the Bay,” a biennial conference sponsored by the Casco Bay Estuary Project.