LAKE WATER QUALITY

Lake

Otago is world famous for its photogenic landscapes, How did your lake score in 2015? the soaring mountain ranges complemented by the Lake Wakatipu 1.48 region’s big blue lakes. Lake Wanaka 1.62 Lake Hawea 1.27 Tourists, holidaymakers and locals alike value our lakes for their clean, clear waters. And we want to keep it that way. INDEX DESCRIPTION RATING Regional Council (ORC) regularly monitors Less Microtrophic the water quality in nine lakes throughout the region, than 2 The lake is clear and blue with including lakes Wakatipu, Wanaka and Hawea. very low levels of nutrients and algae We want you to know how good your lakes are, so you can fish, swim, ski, board or bathe knowing the water 2-3 Ogliotrophic is healthy and safe. The lake is clear and blue, with low levels of nutrients and algae WHAT DOES LAKE MONITORING INVOLVE? 3-4 Mesotrophic Our team monitors lake water quality using a measurement The lake has moderate levels known as the Trophic Level Index (TLI). This value gives us an of nutrients and algae overall picture of the health of the lakes. Depending on its content and clarity, each lake is assigned a 4-5 Eutrophic number between 1 and 5 – the lower the number, the better the water quality of your lake. The lake is green and murky, with higher amounts of A lake’s TLI value is calculated from these four water nutrients and algae quality parameters: Greater Supertrophic ƒƒ Chlorophyll content than 5 The lake is fertile and ƒƒ Total phosphorus saturated in phosphorus and ƒƒ Total nitrogen nitrogen, often associated ƒƒ Water clarity with poor water clarity (not in all cases) Source: https://www.lawa.org.nz/learn/factsheets/lake- trophic-level-index/

Visit www.lawa.org.nz for the latest water quality information on your local lake.

continued over page

LAKE SNOW IS IT HARMFUL? In recent years, a slimy substance called ‘lake snow’ has been found in Lake Although it is not toxic and poses no Wanaka, Wakatipu and Hawea. Otago Regional Council (ORC) is working with known human health risk, it is creating stakeholders and researchers to find out more about where lake snow comes costly problems for water users. If it from, what influences it, and how it could be managed. gets into the residential water supply, lake snow causes blockages, clogs filters and household appliances connected to the system. On the lake, fishermen may find the algae accumulates on their fishing lines and lures. It can also stick to boat hulls and equipment, wetsuits and your skin or hair if you come in contact with it.

WHAT ARE WE DOING ABOUT IT? Along with Queenstown Lakes District Council, University of Otago, and Landcare Research NZ Ltd, ORC Lake snow is a sticky, biological material made up of diatoms – these are single are trying to better understand the cells of algae that form colonies. Lindavia intermedia are the algae species science behind lake snow and its responsible for creating lake snow. increased presence in our lakes. The lake snow algae secretes large amounts of polysaccharide, a glue-like We are currently running a substance, which cause the algae cells and other microscopic organisms to comprehensive lake monitoring clump together on the water surface. programme that will give us detailed information on how many nutrients are in the lake and the overall trophic WHERE DOES LAKE SNOW COME FROM? state of the lakes. We are also The origins of lake snow are currently unknown - it may or may not be a new supporting a study of lake snow algae species to our lakes. Currently it is found in Lake Wakatipu, Lake Wanaka and DNA, to help us determine its origins. Lake Hawea. This combined research will provide It has also been found in Lake Coleridge in Canterbury. In the past, it has been baseline information that will guide found in Lake Benmore, Lake Aviemore and in the our management response to lake and Lake Waikaremoana in the North Island; however it does not appear to be snow. present in these lakes today.

CHECK. CLEAN. DRY. HOW DOES IT GROW? Freshwater pests, including lake There are some suggestions of the reasons behind the rise of lake snow algae, snow or didymo can be spread by a which are linked to both natural and human-made influences. For example: single drop of water or plant fragment. With limited control tools available Climate change effects for some aquatic pests, and none With a changing climate, any increase in temperature, even a subtle one, may at all for others, it is very important produce conditions that favour the growth of different species of algae. to limit and prevent it from invading Land-use changes and increased nutrients other water bodies. ORC employs a Freshwater Biosecurity Advocate to Many lakes have very low Trophic Level Index (TLI) values, which travel around the lakes and popular indicate low levels of nutrients and algae, a sign of good water quality. Because aquatic recreational sites, spreading of this even very slight increases in nutrients in a lake can result in marked the CHECK, CLEAN, DRY message. changes in the algal community. If you are moving your boat from one Water fleas and space lake to another, you must always Water fleas (Daphnia spp.) in the lake may preferentially graze on an algae that CHECK, CLEAN, DRY any equipment typically competes with lake snow algae. The introduced North American water that comes into contact with the flea Daphnia pulex is a more efficient consumer of these competing algae than water, between every waterway, every the New Zealand native water flea, Daphnia carinata. time. This increased grazing pressure from D. pulex may remove more competitor You can also help by letting us know algae than normal, creating a vacancy in the environment for lake snow algae to if you find lake snow in an Otago get the upper hand. lake or waterway other than Wanaka, Wakatipu or Hawea. Report it to us on 0800 474 082

Find us on facebook otagoRC