English fire crews were called out to aid dying fish in Northampton, BBC News reports. Members of the public noticed that fish had died in a lake in Abington Park and notified the authorities. The fire crews pumped up water from the lake and then sprayed it back in an effort to increase the oxygen content in the water.

The Environment Agency is now investigating the cause behind the incident. According to their tests, the problem was not caused by low oxygen levels and might instead be related to weather or disease. “It could have been low oxygen – although we have since found out this is not the case – it could be the hot weather or it could be disease. We don’t know at the moment.” an Environment Agency spokeswoman said to the BBC. The spokeswoman also caution against releasing aquarium fish into the wild since it can spread disease.