Canals have many features in common with ponds and small lakes. They each have open water with small submerged and free floating plants. Nearer the banks transitional emergent vegetation composed mainly of sedges and horsetails stand clear of the shallower water. At the margins these are succeeded by grasses and tall herbs with, in places, some moisture demanding trees such as Alder and certain Willows. In many places these three zones are quite distinct from each other (specialists may recognise further sub-zones). In other places for a variety of reasons the progression from one zone to another breaks down. See if you can pick out the seperate sections and try to account for instances where the transitions do not seem to be taking place.
Left alone, canals, ponds and even lakes will eventually become filled by a combination of silting and vegetational encroachment. In canals, this cannot be permitted and the central water course is kept open by a combination of cutting and dredging. When a stretch of the canal has been cleaned out in this fashion it will look quite unattractive, but provided the cleaning has not been too severe the wildlife quickly recovers.