Blackwater Rail Trail
This is a nice, easy cycle or walk along a disused railway line between Witham and Maldon in Essex. The route passes through the pretty village of Langford and includes views of the River Blackwater and a riverside section along the River Chelmer into Maldon.
To extend your walking you could try the Witham River Walk which heads south along the River Brain to the Whetmead Nature Reserve. Here you can see the confluence of the River Blackwater and the River Brain and look out for a variety of interesting flora and fauna.