Monitoring results

Waihi Beach has been lucky. The Bay of Plenty holiday spot escaped the oil slick that coated much of the coastline after the Rena disaster. But holiday makers would still be wise to watch where they bathe. Three Mile Creek flows into the sea at Waihi and has a permanent health warning to avoid swimming.

Treated effluent from the Waihi Beach Wastewater Treatment Plant flows into Three Mile Creek. But the local council says testing shows far more contaminants enter the waterway from farmland upstream of the plant. Last summer, e.coli counts in the creek jumped to 4700 per 100mls of water – over 8 times the level considered "safe" to swim.

It's a scenario being played out around the country. Our water quality is considered good by international standards; yet pollution from sewage, stormwater and agricultural run-off is threatening many of our rivers and beaches. Unlike the oil slick from the Rena, the immediate effects can be much harder to see.

Results worse

Monitoring results indicate swimming water quality was worse last summer than in the previous year. 58 percent of all bathing sites monitored in 2010/11 exceeded bacteria levels considered "safe" for swimming on at least one occasion (see Testing and grading). That's up from 46 percent in 2009/10.

The Ministry for the Environment reckons the wet weather suffered by many regions last year is partly to blame for the poorer result. Rainfall causes more faecal matter to be washed from the land into the sea. As a result, bacteria levels in our swimming waters can skyrocket.

Tidal flows at coastal sites mean high bacteria counts are more likely to be short-term events. But that's not always the case. For the last 5 years, monitoring of water quality at Auckland's Laingholm Beach, French Bay and Wood Bay has found unsafe bacteria levels more than 30 percent of the time.

Freshwater spots are also more likely to return poor results. 64 percent of the 237 freshwater sites monitored last year had unsafe e.coli levels on one or more occasions. Many sites are on rivers and streams that run through catchments where dairy farming has been expanding.