The processing of consents for TrustPower's hydro proposal on Marlborough's Wairau River shows the need for Resource Management Act (RMA) changes, Environment Minister Nick Smith says.

TrustPower's plans for a $275 million hydro scheme in Wairau Valley was granted resource consents in August last year.

A report on the processing of the consent application said it was difficult for small councils, like the Marlborough District Council, to process major infrastructure consents.