Question: Does the quality of water change with the weather? If so, how often?

Alistair Young answered on 6 Feb 2021:

Nice point! Quality of water is affected by weather … when it is wet and there is a greater volume of water in the river, it flows faster. At different parts of the river, that has different impact – faster flow carries more sediment and erodes the banks more, so the water can get cloudy and disrupt feeding etc for the creatures in the water. Where the river is slower or held back by weirs or blocks of some form, that extra sediment is dropped… and the river bed covered over, which can cause problems for bottom dwellers and bottom feeders. And of course in all this greater volumes of water entering the river will also wash in more pollutants – oil and chemicals from roads and built up areas, fertiliser and perhaps slurry from farmland, and increasingly, sewage overflow from water treatment plants which can’t cope.
Then … if it is dry and there is less water, the problems are different… not enough water to dilute any pollutants or wash them away… algae growing in profusion and absorbing more oxygen to the detriment of creatures.
So overall a balance is best!