Looking at a couple of cottage advertised in Durweston, I should imagine it's only got a short stretch as the south bank is mainly Durweston AC and the island between the weirs is Wimborne AC though the owner may let visitors fish. In the past this area had some excellent roach and chub fishing with some perch and dace but in winter it's subject to high water levels and may not be fishable much of the time - I used to fish the north bank a lot in summer many years ago with casters for big roach but more likely to get small roach now.
Not far upstream Sturminster & Hinton AA have about 10 miles of water with day tickets from a couple of places in the town - see their website - that offers a variety of water that is good for roach, chub and perch with some bream and even, if you're lucky, tench. Some of the river is deep and slow, other parts shallow and fast. No barbel this far up. Float fishing bread punch/maggots for the roach, flake for the chub over liquidised bread. Access can be tricky as many long walks but some easier bits to access. I tend to travel light, leaving the keepnet at home.
Blandford DAC (day tickets from Conyers in Blandford) also have some water just up from Blandford though I haven't fished their water for many years, used to be mainly roach, with the river much bigger than further up.