There are regulations in place which ban disposing of untreated sewage in harbours, within 500 metres of the shore and within 200 metres of a marine reserve. Most of the marinas and regional councils provide information for visiting boaties on the rules and expectations. Maritime NZ also have information on discharge standards.
Hold it – We’re Cleaning Up the Coast published by MfE and Maritime NZ says, the most important thing is “how well the water body, which the sewage is being discharged into, can flush itself”. This is influenced tides, wave action, currents, salinity and temperature of the water. In other words, where you choose to dump sewage from a boat is critical.
The closer the discharge point is to shore, the closer it is to where people are swimming and gathering shellfish as well as marine farms and important ecological areas. In these areas boat sewage poses potential environmental and public health issues.
The Ministry for the Environment (MfE) and Maritime NZ have produced a Guidebook to help boaties chose the best system for their boating requirements.
Discharging Sewage From a Boat
Apparently liquid waste is not a serious problem. Most urine is sterile and therefore little risk occurs from flushing urine directly from an on-board boat toilet. The problem is solid waste.
There is a significant public health risk from discharged sewage. Sewage can contain disease-causing bacteria, viruses and parasites. According to MfE, the biggest concern with boats dumping raw sewage is the spreading of water-borne diseases. These include hepatitis A, giardia, typhoid and cholera.
Of concern is the impact on shellfish and the subsequent risk to the consumer. Filter feeding shellfish, such as oysters and mussels, are very good at concentrating the disease-causing organisms present in sewage. These viruses can survive for a long time in water, sediment and shellfish. This is why the sewage discharge from one boat alone can, if the circumstances are right, have a significant impact on the health risk of a whole bay.
It is obviously not just boaties that are responsible for contaminating waters. Councils are upping the ante on improving both septic tank management and sewage reticulation systems, but there is more expectation on everyone to do their bit.
Sewage Disposal Options for Boaters
Use of shore-based disposal facilities is the best as it keeps all contaminants contained and treats the sewage through a municipal system. This works well with ordinary portable toilets as well as boat holding tanks.
A boat owner may install a sewage treatment system, which electrically alters seawater to treat the sewage. An alternative is installing a boat holding tank and then discharging this when far out at sea. Using biodegradable cleaning and disinfectant products in the boat toilet will reduce the risk of pollution.
There are guidelines available that have tips on operating and maintaining sewage treatment systems and holding tanks. The easiest is to go and talk to a local boating and marine supply shop.
The most important thing is to be vigilant about discharging sewage from boats. Discharging sewage at sea, if there is no alternative, should be done as far away from land as possible and while the boat is moving.
Lucy Brake - Lucy has been working in the environmental industry for the last 10 years, specializing in the impacts of coastal, marine and port ...
