About 200 years ago, North Shore City was an area where nature took care of itself. As people have come to live in the city in ever-increasing numbers, they have changed the environment so much that very little of the city remains in its natural state.

Sources of stream and beach water pollution

Streams

All streams on the North Shore have been modified to some degree. They have been piped, lined or had the vegetation along their banks removed. Most have also had their flow rates altered by development within their catchment i.e. lower flows in dry weather and higher flows after rain.

They have also had contaminants piped directly into them via stormwater from roads and roofs. They have been polluted by accidental spills, people washing cars on the road, washing paintbrushes over stormwater drains or letting grass clippings fall into streams.

This means that many of our streams no longer look natural and can only support species of fish and insects that are tolerant of pollution and can survive with little natural habitat, such as eels.

Lake Pupuke

Lake Pupuke is highly valued as a recreational and a significant wildlife area. While data tells us that the quality of water in Lake Pupuke is generally reasonable, this could change quickly.

Stormwater and wastewater can harm the lake in a number of ways by contributing:

• nutrients that can cause algal blooms

• suspended solids which could make the water murky

• bacteria and viruses that could pose a risk to human health

We need to understand the risks that stormwater and wastewater pose to the lake. We then need to decide on what actions are needed to prevent further deterioration of water quality in the lake.

Marine

Around the North Shore coastline there are different types of environments. We have long lengths of beach which are used for swimming. We also have large areas of mudflats, estuaries and mangroves, all with high ecological values. These different areas face very different issues.

Mud builds up in the estuarine and mangrove areas. When stormwater flows into this environment contaminants such as heavy metals attach to the mud. These contaminants then build up in the mud to levels where they can become toxic. We are carrying out a study to find out the level of contaminants, but we already know from existing information that in certain areas there are levels of contaminants that have the potential to damage the health of some sea life during sensitive life stages.

The issue facing recreational areas is the risk to public health from bacteria and viruses from stormwater and wastewater.