How does pollution show up in The Radiant Way?

Margaret Drabble's The Radiant Way describes the disillusionment of 1980s Britain and, in particular, the loss of the ideals in the 1960s that many had hoped would lead to the breakdown of the British class system. In this regard, the pollution that is mentioned at the canal on page 231 symbolizes what the novel presents as a decaying society.
When Liz and Esther go for a Sunday walk along the canal, Drabble sets the scene as soon as they leave Esther's flat.

Weeds grew tall from cracks between bricks and slabs of concrete: obelisks rear to the right, a gasometer loomed before them.

They then notice that the green water is full of small dead fishes "belly-upward in the sun." They decide it is due to chemical disaster and the result of an overflow from one of the nearby factories.
A little further along the canal, they pass a mentally impaired woman who two men are trying to prevent from going back and scooping up the dead fishes.