Knettishall Heath is a diverse mosaic of habitats with woodland and riverside meadows, as well as large areas of heath. It extends to over 430 acres. It is notable as a reliable site for Breckland birds, with breeding hobbies, nightjars, woodcock, woodlarks and stonechats. Long-eared owls have nested in recent years, but there has only been one sight record of an adult in May 2024.
A former country park, the site is now a Suffolk Wildlife Trust reserve, and a mixed herd of Exmoor and Dartmoor ponies grazes the heath. Parking in the main river-side car park is free up until 10am; there are other (free) parking places around the heath.