An environment agency is in a spot over an alleged release of toxins into Athi River, which has led to the death of thousands of fish.
There is fear that the fish could be sold to unsuspecting customers in Kitengela and Athi River areas.
Residents have blamed the National Environment Management Authority (Nema) for failure to take action against factories that discharge affluent into Athi River despite public outcry.
Residents who depend on the river have been urging Nema to act against firms that discharge poisonous substances in the river.
Mavoko MP Patrick Makau urged Nema and the county's Environment department to swiftly act and come up with a report on what killed the fish.
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"We're not sure whether these poisoned fish have been sold to residents, that's why we are appealing to the relevant authorities to quickly come up with a report," said Mr Makau.
But Machakos County Nema director Sofie Mutemi said they had collected samples of the fish for investigation.
Speaking to The Standard, Ms Mutemi said Nema would go after factories that discharged hazardous chemicals into the river.
