Water quality at the Footbridge November 2017 to April 2018

We published the Horizons Regional Council Summer Water Monitoring ‘traffic light‘ reports in the sidebar of the website from early November 2017 to April 2018. This summer the results generally weren’t as bad as the previous year.

I asked for the relevant data to be sent to me as a spreadsheet: Can I Swim Here Waikawa data for 17-18 recreational bathing season for Waikawa Beach.

Horizons made 22 measurements in that period. 10 were ‘Green’, 8 ‘Amber’ and 4 ‘Red’.

What do the icons mean?

  • [Green] Suitable for swimming – These sites are generally suitable for swimming.
  • [Amber] Caution advised – Usually suitable for swimming but younger children and older people may be at increased risk at times. If potentially toxic algal blooms are present, avoid contact.
  • [Red] Unsuitable for swimming – These sites may be a health risk and are not considered suitable for swimming most of the time.

What’s interesting though is that upstream, at the Waikawa Reserve on North Manakau Road, 21 results were ‘Green’ and the other one was ‘Amber’.

So what is it that reduces the water quality between there and here?

The shag colony just above the footbridge will certainly contribute E. Coli, but we need more data to explain whether they are the sole cause, or what else may be contributing.

First, the Waikawa at North Manakau Road data:

ValueDate Value Red Amber Green
11/6/17 1:00 63     1
11/12/17 10:00 20     1
11/14/17 10:00 20     1
11/21/17 1:00 63     1
11/29/17 1:00 158     1
12/3/17 1:00 20     1
12/12/17 10:00 52     1
12/18/17 10:00 20     1
12/27/17 10:00 86     1
1/3/18 10:00 97     1
1/8/18 10:00 109     1
1/14/18 10:00 118     1
1/24/18 10:00 265   1  
1/29/18 10:00 199     1
2/4/18 10:00 120     1
2/13/18 10:00 122     1
2/19/18 10:00 120     1
2/25/18 10:00 63     1
3/6/18 10:00 110     1
3/12/18 10:00 52     1
3/18/18 10:00 10     1
3/27/18 10:00 10     1
TOTAL   1 21

Next, the Waikawa Estuary at Footbridge data:

ValueDate Value Red Amber Green
11/6/17 1:00 20     1
11/12/17 10:00 110     1
11/14/17 10:00 110     1
11/21/17 1:00 20     1
11/29/17 1:00 285   1  
12/3/17 1:00 169     1
12/12/17 10:00 106     1
12/18/17 10:00 216     1
12/27/17 10:00 364   1  
1/3/18 10:00 4610 1    
1/8/18 10:00 488   1  
1/14/18 10:00 452   1  
1/24/18 10:00 399   1  
1/29/18 10:00 355   1  
2/4/18 10:00 62     1
2/13/18 10:00 6488 1    
2/19/18 10:00 985 1    
2/25/18 10:00 644 1    
3/6/18 10:00 249     1
3/12/18 10:00 146     1
3/18/18 10:00 295   1  
3/27/18 10:00 295   1  
TOTAL 4 8 10

Here they are compared. Note that our readings were almost always higher than those at North Manakau Road.

ValueDate North Manakau Road Estuary at Footbridge Difference Ours was higher
11/6/17 1:00 63 20 -43
11/12/17 10:00 20 110 90 Yes
11/14/17 10:00 20 110 90 Yes
11/21/17 1:00 63 20 -43
11/29/17 1:00 158 285 127 Yes
12/3/17 1:00 20 169 149 Yes
12/12/17 10:00 52 106 54 Yes
12/18/17 10:00 20 216 196 Yes
12/27/17 10:00 86 364 278 Yes
1/3/18 10:00 97 4610 4513 Yes
1/8/18 10:00 109 488 379 Yes
1/14/18 10:00 118 452 334 Yes
1/24/18 10:00 265 399 134 Yes
1/29/18 10:00 199 355 156 Yes
2/4/18 10:00 120 62 -58
2/13/18 10:00 122 6488 6366 Yes
2/19/18 10:00 120 985 865 Yes
2/25/18 10:00 63 644 581 Yes
3/6/18 10:00 110 249 139 Yes
3/12/18 10:00 52 146 94 Yes
3/18/18 10:00 10 295 285 Yes
3/27/18 10:00 10 295 285 Yes

Leave a Reply

Your email address will not be published. Required fields are marked *