The Environment Agency said the low oxygen level in Pittville Lake could be algal bloom or sediment stirred up by rain, or both.
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George Ford booted 24 points as Bath kept the pressure on Northampton at the top of the Premiership with a 39-16 win at rivals Gloucester.
West Country neighbours meet for first time this season at Kingsholm in Premiership.
The funeral of a mother and newborn baby found dead after going missing from a maternity hospital took place today.