The Bevelly Channel, or Great Island Channel, runs behind Cobh from Little Island to Midleton. It is navigable at high tide, but dries out to extensive intertidal mud flat at low water.

These tidal mudflats and salt meadows are habitats of extreme conservation importance. They are very important both to invertebrates and to wintering waterfowl. As a result, the Belvelly Channel is designated as a Special Area of Conservation under the EU Habitats Directive.

The Belvelly Channel is relatively undisturbed and could be described as one of the quieter areas in Cork Harbour. Activities along its shores are mainly agricultural, with some quarries on the northern side. Oyster and mussel beds in the centre of the channel are marked by tall, slim stakes. Foaty Island with the wonderful Fota Wildlife Park, Fota House and Fota Arboretum is adjacent to Belvelly Bridge. Constructed in 1807, this is the only bridge linking Great Island with the mainland.

Belvelly Castle stands on the Great Island side of Belvelly Bridge. This is a typical mediaeval square tower dating from the 15th century and is said to have at one time belonged to Sir Walter Raleigh. Three of the five Martello towers in the harbour overlook the Belvelly Channel. The first is at Rossleague, the second at Belvelly and the third at Marino Point. These towers are larger than their counterparts in the UK and, again unusually, all have straight sides.