The River Glaven becomes tidal below the sluices on the coast road that runs through Cley-Next-The-Sea. The tidal section of the river runs through Blakeney National Nature Reserve (NNR) as managed by the National Trust.
Blakeney NNR consists of a mosaic of world-famous mud flats, reedbeds, saltmarshes, and freshwater marshes (with associated ditch systems) and is one of the most beautiful semi-natural areas of the UK. The NNR supports a host of rare and important wildlife. The channel feeds a tidal reed bed where, during summer months, you can hear Reed Warbler, Sedge Warbler and Cettis Warbler. Further towards the harbour, at low tide, mudflats are exposed, providing feeding opportunities for a variety of waders including Oystercatcher, Curlew and Redshank.
A small off-shoot from the River Glaven diverts flow through Blakeney Freshes; an area of re-claimed saltmarsh isolated from the sea by earth banks. As the name suggests the Freshes is a freshwater habitat – but sea floods are capable of reclaiming it (as in December, 2013). The freshes supports a network of ditches, many of which follows old creek systems where Otter and Water Vole have often been seen. The channel also flows through an area of reed bed, which provides ideal habitat for breeding birds such as Marsh Harrier and Bearded Tit.
Water levels on the Freshes can be lowered at certain points in the system to carry out management to the reed bed and to allow cattle to graze on the marsh during the summer months. Levels can also be raised to provide habitat for over-wintering wildfowl.
At the Western end of the Freshes, the river meets the sea wall, where at low tidal, sluices allow water through, into Blakeney Channel. The sea wall and coastal path around Blakeney Freshes provides a good viewing point for the variety of birdlife on Blakeney NNR. In spring, you may also see boxing Brown Hare on the Freshes.