 Malltraeth Pool at the north end of the estuary is a place visited by many waterbirds during their spring and autumn migrations, and other wildfowl and waders are to be seen on the estuary all winter.Newborough Forest on the southern shore is used by large numbers of ravens as a winter roost, and a peninsular and a rocky islet in the estuary are a breeding ground for shags and cormorants.Migration of fish and eels is effectively blocked by the dam at the Cefni water treatment works, holding back the Cefni reservoir.