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Boat Use Effects Lake Water Quality

5 September 2023

Improving Lake Rotoiti Water Quality

How You Use Your Boat Effects Lake Water Quality

We all enjoy a wide range of boating activities on the lake and we all want to see the safe swimmable standard of the lake improve and endure, so here are a few things we can all do to help sustain and improve water quality to meet this end.

Did you know that many of the biggest threats to clean and safe lake water quality come from boating activities?


The 5 knot rule is in place primarily for safety of water users and to reduce wake damage to the shoreline but as it applies in shallower parts of the lake, it also has a big part to play in reducing propellor damage to weed beds and stirring up bottom sediment. Both of these things introduce nutrients into the water column which accelerate algae and weed growth.

Note that operating your wakeboard boat less than 500M off the shoreline sends a large destructive wake into the shoreline.


Clean boats, clean motors, clean trailers, clean water toys and clean fishing equipment are the first and most important line of defence against spreading unwanted invasive species.

There are three methods to get rid of these and sterilise your boat.

First, launch in full strength salt water and run your motor at least until hot.

The second most effective way is to leave your boat parked and dry for six or more months and ensure that the motor cooling system and bilges are drained of all freshwater.

Third, clean your whole boat, trailer and motor with cleaners like Simple Green, disinfectant, detergent, bleach or other chemicals as it is hard to get into every tiny nook and cranny, especially if your boat has ballast tanks. Fishing equipment & water toys are relatively easy to clean with a chemical agent.

Launching in multiple lakes & rivers

If you have recently used your boat in a river or another lake, don’t launch in the Rotorua lakes until you have sterilised your boat, trailer and gear as above. For example, if you have recently been boating on the Waikato River, there is a high risk that you could be responsible for introducing the Gold clam or other seriously invasive species that are notcurrently in our lake system. In fact these species can only be introduced by boats, fishing tackle and water toys. Similarly, don’t launch your boat in more than one lake without sterilising between.


Your boat’s propeller and wake inject oxygen into the water. Algae and lake weed benefit from this extra oxygen. Because of this, excessive speed close to shallow areas and shore has a negative effect on water quality.

We all care about the safety and quality of the water in our lake and sometimes the problem feels like it's too big and nothing we do can make a difference. These suggestions are things we can do that will make a difference to ensure that our lake is a safe place for all, forever.