A deposit of sand forming a shallow area in the sea or a river.Shoal water is an area made shallow by a sandbank or sandbar....
I know now, that the place names in shipping forecasts are usually sandbanks, river estuaries, and those types of things.
The new hovercraft, designed to be used on mud and sandbanks as well as shallow water, was unveiled at the RNLI lifeboat station in Morecambe, Lancashire.