Toxic Algae Alerts & Monitoring

The alert level is based on an assessment of the percentage of river bed covered by cyanobacteria mats at each site. Risk may also be increased by algae mats carried downstream from other sites. Check regularly to stay informed and look out for any warning or information signage. 

Alert level Health risk
exposure to cyanobacteria toxins		 Cyanobacteria present Action
Low (Green) Low Zero to 20% Most parts of rivers will not have cyanobacteria. Take usual care and be aware of cyanobacteria and risks
Medium (Amber) Low to moderate 20-50% Blue-green algae levels have increased due to warm settled weather. Keep children and dogs away from the river and its margins where they may come in to contact with algal mats
High (Red) High 50%+ Blue-green algae levels have increased to warning level due to warm settled weather. Do not swim and keep children and dogs away from the river and its margins where they may come in to contact with algal mats

Information about what to do during the different alert levels can be found in the Frequently Asked Questions.

Phormidium cyanobacteria % cover at river monitoring sites (note: < = less than) 
Date Maitai at Avon Terrace Maitai at Dennes Hole Maitai at Campground Wakapuaka at Hira Reserve Isel Park

2024 (< = less than) 

15 March 2024

 <1% <1% <1% <1% <1%

4 March 2024

 0% 0% 0% <1% 1%

23 February 2024

 o% 0% 0% 2.5% 2.0%
7 February 2024 <5% <5% <5% <5% --
5 February 2024 <5%  <5%  <5%  -- --
19 January 2024 4% <1% 3%   2%
4 January 2024 4.5% <1% 7.5% <1% <1%

 

2022/23

27 December 2023

 <5% <1% <1% <1% -

22 December  2023

 13% low risk <1% low risk 16% low risk  - - 
15 December 2023 16.5% 2.5% 15% 0.5% 2.5%
29 November 2023 6.25%  <1% 6.75%   0%
9 November 2023 25.5% 1% 7.5% - -
6 April 2023 0% 0% 0.1% 3.25% 0%
8 March 2023 <1% 0% <1% 6.5% 1%
1 March 2023 <1% 0% 2.75% 10% -
24 February 2023 <1% 0% 5.5% - -
22 February 2023 - - - - <1%
15 February 2023 2.5% 0% 1.5% 4.5% <1%
10 February 2023 <1% <1% <1% 3.15% <1%
3 February 2023 1.5% <1% <1% 5.5% -
25 January 2023 3.75% <1% 3.5% 2.5% <1%
18 January 2023 7.5% 1% 8% 4.3% -
13 January 2023 - - - - <1%
12 January 2023 18.75% - 3.75% - -
11 January 2023 17.25% 1.75% 4.5% 1.25% -
4 January 2023 21% - 12% <1% -
28 December 2022 32.72% 2.6% 6% <1% -
23 December 2022 22.5% <2% 7% - <1%
21 December 2022 29.25% - - - -
20 December 2022 - 5.5% 12.5% <1% -
15 December 2022  22.25% - - - <1%
14 December 2022 - 9% 9.25% - -
12 December 2022 16.5% - - - -
2 December 2022 14% 6.25% 4.1% <1% <1%
25 November 2022 11.35% 2.1% <1% 0% 0%
17 November 2022  5.55% 5.25% 3.6% 0% <1%

11 November 2022 

 3.25% - <1% - <1%

11 March 2022

 <5% <5% <5% <5% <1%
9 March 2022 - - - <5% -

4 March 2022

 - - - - <1%

18 Feb 2022

 1% 2% 6.8% - <1%

28 Jan 2022

 0% 0% 0% 4.7% <1%

21 Jan 2022

 - - - - <1

19 Jan 2022

 - - - 12.5 -

17 Jan 2022

 0 0 0 - -

 5 Jan 2022

 10.45 3.5 35.75 8.85 <1

 

2020/21

29 Dec 21

 35.75 12.75 44.25 2.4 not sampled

24 Dec 21

 40 26 49 3 <1

14 Dec 21

 14.75 21.5 35.75 <1 <1

2 Dec 21

 49 19 43 <1 -

26 Nov 21

 36.85 16.85 32.95 1 -

16 Nov 21

 13 9 32.5    

8 Nov 21

 8.75 3.25 32 0  

15 Feb

 2 0 0 5.75 20
4 Feb 0.5 0 0 10.5 7.25
20 Jan 2 0 0 8.75 0.75
7 Jan 20.75 0.5 0.75 8 3.25
30 Dec 21.3 4 4 3 2.35
15 Dec 41 21.25 23.5 0.25 0
7 Dec 29.5 28.5 26 1.25  -
Phormidium cyanobacteria % cover at river monitoring sites
Date Maitai at Avon Terrace Maitai at Dennes Hole Maitai at Campground Wakapuaka at Hira Reserve
2019/20
6 Mar 0 0 0 0.25
28 Feb 0 0 0 0.25
14 Feb 0 0 0 2
5 Feb 2 2 0 15
29 Jan 0 0 0 0
24 Jan 2 0 0 1.25
13 Jan 15.75 16.75 20.25 5
7 Jan 16.5 20 21.5 1.5
3 Jan 10 5 15 2
31 Dec 12 25.5 28 5
24 Dec 9.5 16.75 13.75 2
11 Dec 16.25 13.25 14.75 0
6 Dec 2.55 5.75 5 0
29 Nov 21.25 7.75 21.25 0.25
19 Nov 10.25 7.75 11.25 0
19 Mar 0 0 0 0
12 Mar 0 0 0 0
27 Feb 0 0 0 0
15 Feb 0 0 0 0
8 Feb 0 0 0 0
1 Feb 0 0 0 0
25 Jan 0 0 0 0
18 Jan 0 0 0 0
15 Jan 0 0 0 0
3 Jan 0 0 0 0
2018
27 Dec 0 0 0 0
20 Dec 0 0 0 0
17 Dec 6.6 1.75 1.75 3.25
3 Apr 7.75 1.25 4.75 1
21 Mar 10.25 0.5 2.5 3
14 Mar 7.75 0.5 1.5 2.5
7 Mar 3.25 0.25 1 1.75
28 Feb 3 0 0 0.25
22 Feb Not surveyed due to high flows
15 Feb 0 0 0 0
7 Feb 13.25 0 0 2
31 Jan 9 0 0 1.75
24 Jan 0.75 0 0.5 0.25
17 Jan 0.25 0 0 0.75
10 Jan 0.25 0 0 0.25
3 Jan 0.5 0 0 1.25
2017
27 Dec 0 0 1.75[dm] 1[dm]
20 Dec 2.25[dm] 0.75[dm] 9.5[dm] 2[dm]
13 Dec 7[dm] 2[dm] 13.5[dm] 3.75[dm]
6 Dec 15 [dm] 2.75 [dm] 18.75 [dm] 2.25 [dm]
29 Nov 25 4.75 17.8 3.5
22 Nov 31 6 14.25 4.25
15 Nov 28 9 15.5 3.8
10 Nov 18 14 10.25 2.75
29 Mar 10.75 0 0 2.75
22 Mar 7.75 0 0 1.5
16 Mar 3.75 0 0 2
9 Mar 5.5 0 0 1.5
1 Mar 5.25 0.5 0 1.75
23 Feb 7.75 0.75 0 2.75
15 Feb 8.25 1.25 0 2
9 Feb 7.5 1.25 0 2
1 Feb 4.25 2 0.5 1
26 Jan 0.5 2 0 0
18 Jan 15 15 0 0
11 Jan 16 14 3.5 0.5
4 Jan 16 17.5 3 0
2016
28 Dec 14 12.5 2 0
21 Dec 23.5 21 12.5 0
15 Dec 21.5 17 8.5 0
6 Dec 23.5 17 11 0
30 Nov 21 12.5 6.3 0
21 Nov 3 6 3 0
16 Nov Not surveyed due to high flows
9 Nov 28 22 3 2
18 Oct 12 [High Flows] 4 0

[dm] : detaching mats