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 |