Loch Fergus is a freshwater post-glacial 'Kettle Hole', situated in a low lying area close to the B742 road between the farms and dwellings of Trees, Lochfergus and Bowmanston. The loch drains to the southwest into Snipe Loch. Tradition states that the name is derived from King Fergus, one of the Scottish kings who defeated King Cole or Coilus, king of the Britons, in the adjoining fields. The story goes that King Cole and his army were encamped in the vicinity of Loch Fergus and King Fergus attacked them, taking advantage of their drunk and 'feasted' condition. King Cole and his defeated army escaped across the Water of Coyle, only to be caught, defeated, and the King himself killed near Failford.

In 1628 the two merk land of Lochfergus was leased to John, Lord Loudoun for 8s Scots. In the late 17th century the lands passed to the Cassillis family. In 1798 Archibald, Earl of Cassillis possessed the loch lands. The land around the loch is marshy and Lochfergus Wood has been a feature for many years, mainly located on the north-west side. A boat house, reached by an artificial inlet, is marked on the first OS maps not far from the road, reached by an access lane branching of the nearby B742. This feature is missing from the maps by the 1890s.

The roughly oval island is said to have been reached by a causeway, no longer extant, that ran from the bank near Lochfergus Farm. Two totally formless low mounds of boulders are located on the island which may be the remains of a building. The 25 inch OS map indicates a small rectangular structure near the centre of the island. An anglers club-house was constructed in 1976 ten metres from the ruins. The island is covered in dense vegetation. The island is designated by the Scottish Wildlife Trust as a Local Nature Conservation Site (LNCS) and maps show that it has long been covered in woodland.

It is recorded in the 'Chronicles of Scotland' of 1624 that a friary existed on the island and Ayrshire Love refers to local placenames such as Abbothill and Friarland in support of this. The island does has a number of stones scattered over it, however this fact may have led to the friary or monastery legend. The remains have also been suggested as relating to wildfowling, such as being the ruins of a duck decoy or such-like.

Nothing now remains of the Kennedy's hunting lodge, recorded as 'an old ruined castle...which probably was used as a shooting station by the Cassillis family' which is said, in 1837, to have stood near the margin of Loch Fergus near the track running off the B742. The RCAHMS designate it as a Tower House and it is not clear when it was built.

An old trackway known as the 'Foul Calsey' used to run from Loch Fergus past Trees, Macnairston, and Crofthead to Ayr, joining the Cumnock Road near Holmston. This road was still used up until the 1920's at harvest time. Farmers later cleared away tracks like this because they denied arable ground to them and could damage their ploughs.