Holland Haven Marshes is a 208.8-hectare (516-acre) biological Site of Special Scientific Interest north-east of Clacton-on-Sea in Essex.

It is an L-shaped site which stretches along the coast from Frinton-on-Sea to Holland-on-Sea, and then north along the Holland Brook.

[1][2] It includes Holland Haven Country Park, a 22.1 hectare Local Nature Reserve owned and managed by Tendring District Council.

[3][4] A network of ditches radiates from Holland Brook, and these have several nationally scarce aquatic plant species, such as brackish water crowfoot and divided sedge.

There are also rare invertebrates, including the Red Book soldier fly Stratiomys singularior.