Otago’s first toxic algal bloom for summer spotted at Butchers Dam

Media Release - 01 December 2023

ORC’s environmental monitoring team have collected samples at Butchers Dam in Central Otago that show the presence of cyanobacteria (toxic algae). Upon inspection today, it was noted that the bloom is still present and appears worse than last week.

ORC staff are waiting for results from further testing to confirm the alert level but feel confident in issuing a warning with the probability people will be out and about on the first weekend of summer.

“Given the staff observations this week, the previous history at the site and the continuous presence of cyanobacteria scums over the last week or so we decided the warning was warranted,” says ORC Scientist, Water Quality and programme lead, Helen Trotter. 

This kind of algae is potentially toxic (and can be deadly) to both humans and animals. Dogs should be kept on a leash to steer them away from the water, and those visiting Butchers Dam for recreation should stay out of the water until it is confirmed safe to swim here.

Warning signs have been erected in the area to make visitors and residents aware that the water at Butchers Dam is unsafe for swimming, drinking and it is recommended to keep pets and stock away. 

To find the latest toxic algae sightings, go to: www.orc.govt.nz/toxicalgaesightings

Pea soup appearance of water shows algal bloom

Algal blooms and pea soup-like appearance that can suggest toxic algae is present

ORC’s recreational water monitoring programme begins on Monday 4 December, and will test popular swimming sites to make sure water is safe for swimming.

This summer ORC will test 33 swimming sites weekly for bacteria and 11 sites for toxic algae.

The latest water quality results are then posted to lawa.org.nz/swim (Land Air Water Aotearoa), a handy resource for New Zealanders across the country to check the quality of their favourite local waterway.

“Every year ORC’s water scientists check popular swimming spots around Otago to see if these rivers, lakes and streams are safe to swim in.”

“While we monitor water quality weekly at a number of Otago’s most popular sites it is important people remember that water quality and conditions can change quickly especially after rain. That’s why wherever you chose to swim it’s always advised to wait at least two days before swimming after heavy or prolonged rain,” says Ms Trotter.  

The Otago programme, which started in 2006, runs during the summer months from 1 December to 31 March.

Warning Sign in place at Butchers Dam

Warning Sign in place at Butchers Dam

The ORC team visits sites weekly to take samples, the results of which are posted to LAWA.


A screenshot of the map on LAWA’s website showing favourite swimming spots throughout Otago.

“Plenty of other council monitoring programmes across New Zealand continue to grow, with almost 800 recreational swim sites now on the site.”

People can find out if a swim area is safe on LAWA, by clicking on the swimming icon on the orange box, top left, or by selecting the menu option under the search bar that says, “Can I swim here?”

This way people can search for their local water ahead of a visit and plan their trip with the latest information. The map will show spots which are suitable, or not, for swimming using the handy traffic light system.

As well as test results the LAWA website has lots of useful factsheets, which can be found using the search bar, including the swim safe checklist and how to spot toxic algae.

Back to top
Online Maps & Data: