Overflows (into public or private property, waterways and the sea) can occur as a result of wastewater overflowing gully traps, manholes, engineered overflow points, or pump stations.
They occur when the wastewater system has been overloaded with water, typically after a heavy rainfall event.
To avoid wastewater overflows ensure you are only connecting wastewater plumbing to your gully trap. Any stormwater from outside, including roofs, retaining wall drains, driving strip drains, basement pumps or paved area drains, must be diverted to a soak pit or stormwater lateral to road kerb.
Note: It is also recommended you do not swim for two days following a heavy rainfall event. This is to not only protect you from wastewater overflows, but also other contaminants from stormwater that wash off the roads.
If you want to know what the water quality is at your local swimming spot, check out Greater Wellington Regional Council's 'Is it safe to swim?' map.