Teesmouth is a National Nature Reserve with a difference, it is surrounded by one of the largest concentrations of heavy industry in Britain. The reserve covers 350 hectares in two sections separated by Hartlepool Power Station. North Gare lies to the north and Seal Sands to the south.
At any time of the year, interesting birds can be seen. Migratory ducks and waders have always visited the estuary. In winter, Knot from Greenland and the Canadian Arctic, Shelduck, Teal and Sanderling are seen. In spring, Ringed Plover, Lapwing, Oystercatcher and Snipe nest. Sandwich Terns, having bred further north, stay for a few weeks during July and August. Cormorant, Curlew and Redshank arrive in large numbers for the autumn.