Rutland Water is a man-made reservoir located near the market town of Oakham. It is considered one of the best places to go birdwatching (particularly for waterfowl) in the UK due to the vast wetlands, woodlands and grasslands.
In winter, there can be in excess of 25,000 ducks, geese and swans at Rutland Water.
When visiting, your best bet is to go to the Anglian Water Birdwatching Centre, which is located at Egleton Nature Reserve. You can expect to visit over 30 bird watching hides. There is a mixture of nature and walking trails too.
You'll need a permit to access the reserve, for more details visit here.