Tewinbury is a 7.5-hectare (19-acre) biological Site of Special Scientific Interest near Tewin in Hertfordshire.

The local planning authority is East Hertfordshire District Council,[1][2] and the site is managed by the Herts and Middlesex Wildlife Trust[3] The site borders the River Mimram.

There are areas of swamp and tall fens, with plants including butterbur and angelica.

There is a lagoon which has a two storey hide for observing birds and water voles.

[1][3] Access to the site is in the drive to the Tewin Bury Farm Hotel on Hertford Road.