By surface area it is the largest reservoir in England, but its capacity is exceeded by that of Kielder Water in Northumberland.

Because much of the valley is clay, material for the dam was extracted from pits dug within the area that would be subsequently flooded.

At its base, it is up to 890 yards (810 m) wide, and the finished structure has been landscaped to blend in with the environment, even when viewed from Empingham, the nearest village.

Large areas of wetland (as well as several small woods) at the western end of the lake form a nature reserve, managed by Leicestershire and Rutland Wildlife Trust.

Other birds found here include lapwing, coot, goldeneye, tufted duck, pochard, teal, wigeon, cormorant, great crested grebe, little grebe and, most notably, osprey, which were re-introduced to the area during 1996,[11] including one called "Mr Rutland".

[12] The lake is stocked with brown trout and rainbow trout, but there is a large head of coarse fish populated by water pumped in from the River Welland and River Nene, species include roach, bream, pike, zander, perch, eel, wels catfish and carp.

In early 2021 an ichthyosaur fossil was discovered during the routine draining of a lagoon at the reservoir by nature reserve manager Joe Davis.

A Temnodontosaurus with a skeleton measuring about 10 metres in length and a skull weighing about a tonne, is the largest and most complete fossil of its kind found in the UK.