It is an earth dam with a core of puddled clay, the inner wall is concreted to mitigate erosion by wave action.

The original plant comprised four circular accelerators, as the demand increased so vertical flow softening tanks were installed from 1970 to 1973.

It is then dosed with lime and pumped to the base of one of eight  gyrazurs – a granular contact mass reactor – where carbonate is removed.

Water is then dosed with sulphuric acid to reduce alkalinity and flows to dual media sand filters where remaining particulates are removed.

There are many footpaths in the woodland around the water where wildlife can be seen, and hides have been erected, with views of the visiting and resident birds.

The water is regularly stocked with rainbow trout; the heaviest fish ever caught, in 1998, weighed 24 lb 1 oz (10.9 kg).

[6] There are two cafés at each end of the reservoir: the newer, opened in 2007, is next to the fishing lodge with a deck overlooking the water, and the other is at the Essex Wildlife Trust visitors' centre.