[4] The SSSI includes ten former gravel pits, part of the Small River Lea, a further waterbody, Hall Marsh Scrape, which was constructed specifically for use by waterfowl.

[1] The various pits support varied aquatic and marinal flora including the nationally scarce whorled water milfoil.

[1] Several pits have developed marsh and rank grassland, their principal value is for invertebrates, particularly an area close to Bowyer's Water where grasshoppers and bush-crickets are present.

This orthopteran fauna is believed to be the richest in Hertfordshire and includes several species more associated with coastal sites, such as the lesser marsh grasshopper and the nationally scarce roesel's bush-cricket.

[1] Several areas of former gravel pit have been infilled with power station pulverised fuel ash, much of which was transported to the site by barge via the River Lee Navigation.

[1] The site also supports a wide range of mammals, reptiles and amphibians: including otter, harvest mice and a large population of grass snake.