The Hawke's Bay Regional Council has been forced to halt drainage work near Puketapu after the death of dozens of native eels.
A video circulating on social media showing a pile of dead eels on a grassy bank sparked outrage online on Monday.
It was not immediately clear whether they were shortfin eels, or the more endangered longfin eels.
One Facebook user said the drainage work was essentially "annihilation of eels and their habitat". Another said it was "disrespectful to one of New Zealand's native fish".
Hawke's Bay Regional Council spokesman Chris Dolley said as soon as it was made aware of the issue surrounding the eels, work was stopped until a full review of the standard work practice could be completed during the coming days.