Local Green Party member and Tauranga City Council mayoral candidate Ian McLean said it would be hard to find a solution for the water quality issues at the eight sites.
Pollution at the Wairoa River wasn't all the fault of humans and some of it was natural, he said.
"Some comes from farming but it doesn't drain a lot of dairy. It makes it a very difficult problem to deal with because it's draining out of forestry and naturally. It may not have been very good water quality in the first place."
Bay of Plenty Regional Council science manager Rob Donald said a number of projects to improve water quality were already underway but generally speaking, unless there were known point source discharges it was not possible to quickly fix those sites that were ranking poor.
He said even by excluding stock from waterways, there would still be contamination from pasture during rainfall.
Mr Donald said the main reasons for the low water quality at these sites were generally farming related, but sewage, wildfowl and wild animals could also cause problems.
People should not bathe in a river if it was discoloured or after rainfall, he said.
Water quality ratings
Very good:
Anzac Bay Bowentown Domain
Kaituna River (Trout Pool Rd)
Mount Maunganui Ocean beach Surf Club
Omanu Beach
Omokoroa Beach
Papamoa Beach Surf Club
Pukehina Beach Eastern car park
Tanners Point Beach
Poor:
Ngamuwahine River (reserve)
Pongakawa River (SH2)
Waihi Beach 3 Mile Creek
Wairoa River (below McLaren Falls Dam)
Wairoa River (Bethlehem)
Waitui Reserve
Very Poor:
Greerton Park (footbridge)
Kaiate Stream (Kaiate Falls)