Kerse or Carse Loch is a natural freshwater loch situated in a phenomenon known as a kettle hole, formed from melting glacial ice. The names Kerse, Carse, and Cars in Scots refers to Low and fertile land; generally, that which is adjacent to a river or water body. The name appears to have originally referred to 'flat lands’ of a wet fenny and character, later associated with rich fertility.

A burn running from the west is sometimes shown on older maps as feeding the loch.   In 1832 Thomson's map shows the 'Carse Loch' with a small inflow burn and a 'Carse' marked as a dwelling on a road to the east.   Curling matches are recorded as having taken place at the loch in 1846 and 1874.

The loch today is mainly fed by rainfall and runoff and the Loch Kerse Burn runs down to eventually join the Water of Coyle. Unusually no water mills appear to have been sited along the burns length. The Kerse Burn has been canalised and deepened along its length to reduce the level in the loch. By 1978 the railway close to the southern loch shore had been lifted and a boathouse had been established on the northern bank. The loch in 1846 was well stocked with pike, perch, and eels, and was frequented by wild-duck, teal, widgeon, and other aquatic fowl. The loch today is part of the Wetland Bird Survey (WEBS).

Kerse Loch lies below Broom Hill and the heights of the Craigs of Kyle, and on its banks is supposedly the site of old Kerse Castle, one time stronghold of the Craufurd clan,  before the family moved to nearby Skeldon House. The old maps however consistently show the castle as lying well to the east of the loch beside the Bow Burn and the surviving physical evidence locates the castle here. The first record of the castle is from 1281 and its final demise is said to have been in 1797 when its ruins were finally blown down in a storm.

 A legend linked to the loch and castle is the 'The flitting of the Sow' which relates to ongoing feuds between the Kennedys of Carrick and the Craufurds of Kyle. Three days before Lammastide, namely the 29th July, Gilbert Kennedy came to Kerse Castle and informed the old Laird of Kerse that his clan would be tethering a sow on their land on Lammas Day. This insult and challenge resulted in the clans gathering all their supporters and on Lammas Day, August 1st, the lairds eldest son, Elspin, lead the clan into battle against the Kennedys on the Craufurds lands at the holms of Skeldon. In the ensuing fighting, John the lairds other son, was killed however the Craufurds eventually drove the Kennedys back into Carrick, a number drowning in the River Doon as they tried to escape.

The old laird had been too infirm to take part and had remained impatiently at the castle looking out over the Kerse Loch for any sign of a messenger from Elspin. At last a rider came into sight and the report was that his son John had been killed, however the Craufurds were triumphant and the sow had been flitted (removed). Alexander Boswell of Auchinleck, a descendent of the combatants, wrote a poem upon the subject, entitled Skeldon Haughs; or, the Sow is flitted.