The River South Esk catchment is a long narrow catchment, draining approximately 564 km².

The headwaters of the River South Esk begin high above Loch Esk on the slopes of Cairn Bannoch in the eastern Cairngorms, at an altitude of 1012 m. From here the water flows into Glen Clova, where it is joined by the White Water below Glen Doll. Further downstream, the Prosen Water significantly adds to the size of the river before it passes through the fertile soils of Strathmore, and from there it flows into the unique enclosed estuary of Montrose Basin, before finally entering the North Sea through Montrose Harbour.

The River South Esk is ~49 miles long (79 kilometres) from its source to the sea, and has four main tributaries:

• White Water;
• Prosen Water;
• Burn of Glenmoye; and
• Noran Water.

The major standing waters in the catchment are:

• the hill lochs of Loch Esk, Loch Brandy, and Loch Wharral in Glen Clova;
• Den of Ogil and Glenogil reservoirs;
• Dun’s Dish; and
• the vast enclosed estuary of Montrose Basin.

Montrose Basin lies at the foot of the catchment and covers 750 ha of tidal mudflats. The tide pushes a staggering 13,600,000,000 l of water from the North Sea, in and out of the Basin twice daily!