New research suggests keeping our freshwaterways clean will remain a long-term mission

From around 3,000 sites, about two thirds of streams and rivers have impaired ecological health, while a third showed impaired water clarity because of sediment.

It also found almost 70 percent of upland deep lakes are in fair, good or very good health.

But Cawthron Institute freshwater scientist Dr Roger Young, says runoff from urban and rural areas remains one of their biggest poblems.

He says the biggest challenges are primarily in pastoral and urban lowland rivers, and in lowland and shallow lakes.