Definition: Generate an appropriate title for the given text. The generated title must be short and include the main topic of the text. The preferred titles are under fifteen words.
Input: Natural Resources Wales (NRW) said more than 500 dead fish were found in the River Cain, a tributary of the Vyrnwy near Llansantffraid-ym-Mechain. NRW officers said the likely source was drainage of a wildlife pond and wetland by a landowner. It is thought nutrients in this water reduced oxygen levels in the river. Rob Ireson, senior environment officer at NRW, said: "Draining water from a pond to a stream may seem quite harmless - but it is what probably wiped out most of the fish on this stretch of the Cain. "The water may look and smell normal - but it can be lethal for fish." NRW said it was likely the fish suffocated when the drained water - which they believe contained low levels of dissolved oxygen and carried nutrients that could reduce oxygen levels even more when they break down - mixed with the river water.

Pollution which killed 500 fish in Powys river identified