The River Mersey estuary runs between Liverpool and the Wirral, with Liverpool on the west bank. It's usually brown in colour, due to the strong currents which whip up the sand as the tide runs and out. At the turn of the tide the river reverts to a greenish colour for a very short time.

The unusual shape of the estuary creates a narrows between Liverpool and Birkenhead of 0.7 miles wide. The strong currents force a deep channel at this point, a tidal scour. Once past this point the current slows up as it enters the bulbous wide estuary beyond. The currents deposits sand into the wider estuary which 3 miles at its widest. The River Mersey has the 4th highest tidal rise in the world.

Fish has returned to the river in abundance, with salmon reaching as far inland as Stockport and Atlantic grey seals as far inland as Warrington. Previously, heavy pollution mainly from chemical plants upstream, reduced fish in the river.

There is talk of damming in the river and creating a tidal power station, as the river is ideal for this sort of power generation.

To see which ships are on the river in real time here. The comings and goings on the river are on twitter.