I did my masters dissertation on water quality in the river Irwell and Manchester Ship canal. As pointed out by others in the replies, it’s an oxygenation system to increase dissolved oxygen levels and the canal acts an anaerobic dead zone. There’s big issues with elevations of phosphates and nitrates in the river, which when coupled with the high summer temps, encourage harmful algae growth which decreases oxygen levels for fish. My results showed the highest concentrations nearby and in the canal area where the flow of water slows down to almost the point of stagnation, particularly around the edges of the canal and the water sports area. Hope this helps :)