The department's director, Friday Njaya, has told Zodiak that samples of dead fish have already been taken to the laboratory to be examined.
Njaya has since urged the people not to eat the fish since investigation is still underway.
"We have received reports from some villages in Makhuwira area that many dead fish were seen flouting on Shire river. The water flowing in the river is dark while the dead fish are yellowish which makes us suspect of some chemicals," said Njaya.
Winston Julius from Nyambalo village and Ward Councilor of Makhuwira North Alex Ziggy Mlonya said the fishermen and some villagers used canoes to collect the dead fish which they were selling in the area.
"We ask authorities to help us as we are not sure on what has killed the fish," said Mlonya.