Our good old river

How might we get the Waikawa Stream back to being clean and swimmable?

We know that the Waikawa Stream isn’t as clean as it used to be (The river runs red), and many of us have our suspicions about why that might be, though we lack the data to confirm the sources of the problem.

Water quality at the footbridge, summer 2016-2017.
Water quality at the footbridge, summer 2016-2017.

The article Troubled Waters in the New Zealand Geographic is a long and careful look at contamination in New Zealand rivers and makes many very interesting points. I suggest you set aside half an hour and read it.

The conclusion of the article is particularly interesting and gives us some useful ideas:

Young believes that correct diagnosis coupled with professional support can lead not just to an immediate improvement in river health but long-term benefits in preventive care. In the Sherry River catchment, for example, the shock of landowners and residents at finding their beloved stream was, in fact, a microbial health hazard galvanised the community to form a catchment group.

Cattle crossings were bridged, leading to a 50 per cent improvement in water quality. Five kilometres of waterways were fenced, and 4000 trees, shrubs and grasses planted in riparian margins. Multiple other measures to control run-off and limit soil erosion were implemented, leading to the group receiving environmental awards in 2009 and 2013.

The community’s enthusiasm for their local river had another benefit: they published their story as a case history. Others can now refer to this “medical literature” and learn from the Sherry River experience.

Sometimes now the Waikawa stream is not swimmable. Next we need to know why and then we can start working on the changes needed to get it back to the safe and fun river so many have enjoyed over the years.

Boat Day 2012.
Boat Day 2012.

The river runs red

In the summer of 2016–2017 the river by the footbridge often had elevated levels of dangerous E. coli.

Waikawa Beach is a popular spot for swimming, kayaking, fishing and puddling about in the water. Each summer the water is tested weekly at various spots around the country, including at and near Waikawa Beach.

Water monitoring spots at or near Waikawa Beach.
Water monitoring spots at or near Waikawa Beach. Source: https://www.lawa.org.nz/explore-data/swimming

Land Air Water Aotearoa say:

Summer season monitoring: Many councils monitor popular recreational sites weekly over the summer months. This lets swimmers know what the most recent bacteria (E. coli) levels were. Remember, even for sites where the monitoring has shown an acceptable to swim test result, some conditions can make them unsuitable to swim in from time to time and we recommend that you avoid swimming after heavy rainfall for 48 hours.

Note: The quality of water for swimming is determined by measuring ‘faecal indicator bacteria’ (enterococci in coastal waters and E. coli in rivers and lakes) which indicate the levels of disease causing organisms in the water.

See Factsheet: Coastal and freshwater recreation monitoring for details of the numbers and risk levels.

An E. coli count below around 260 or an enterococci count below around 200 is acceptable. Above that moves to Alert or Unacceptable. Acceptable counts have been marked in bold and green in the table below.

Water quality at the footbridge, summer 2016-2017.
Water quality at the footbridge, summer 2016-2017.

In the table below, columns are for Waikawa at North Manakau Road (E. coli), Waikawa Estuary at Footbridge (E. coli), and Tasman Sea at Waikawa Beach (enterococci). There’s no rainfall or river flow data in the table, but personal observation is that this summer was exceptionally rainy.

Notice how the water up the road at North Manakau Road is very often green, or acceptable, while some 7 to 10 Km downstream here by the footbridge it’s very often not green. In the sea though seems to be mainly OK.

Sample Date N. Manakau Footbridge Beach
02/11/2016 550 12
09/11/2016 250 96
16/11/2016 2500 24
23/11/2016 900 4
30/11/2016 440 180 24
07/12/2016 25 300 88
12/12/2016 30 260 4
20/12/2016 80 940 60
29/12/2016 25 3300 8
05/01/2017 21 190 120
10/01/2017 150 330 16
17/01/2017 16 190 28
25/01/2017 38 170 300
31/01/2017 81 200 28
08/02/2017 16 560 52
14/02/2017 53 230 56
21/02/2017 75 180 4
28/02/2017 70 220 12
07/03/2017 68 330 60
14/03/2017 48 360 28
21/03/2017 1000 290 4
28/03/2017 63 130 20
04/04/2017 900 2500 420
11/04/2017 34 1300 4
19/04/2017 30 340 4
27/04/2017 92 52 4

Blue water by the footbridge.
Blue water by the footbridge.

After rain and at high tide the river's muddy.
After rain and at high tide the river’s muddy.

More detailed research on all of this and on ways to clean up our swimming water would be an excellent thing.