Update on toxic algae
Summary of toxic algae 2018/19
The good news is that we have not yet had a toxic algal bloom (more than 20% cover) this summer at any of our monitoring sites. Every time it looks like toxic algae might exceed guideline levels (more than 20%) we seem to have a timely rainfall event, such as the rain on Friday night that flushed out the Otaki, Waikanae and Ruamahanga rivers.
Current toxic algae
Hutt River: As of this morning (23 January) there was about 13 % cover at Silverstream and less than 5% cover at Melling and Birchville, and no detached mats.
Kapiti Coast: Results from the Otaki and Waikanae rivers are pending but given rainfall over the weekend it is likely to be free of toxic algae.
Ruamahanga: The Waipoua and Ruamahanga rivers will be monitored today. However, the Waipoua River was checked yesterday as a part of another programme and was assessed to have about 10% cover and no detached mats.
Region toxic algae alert/action level
When toxic algal mat cover is greater than 20% of the riverbed and/or detached mats have accumulated along the river or stream edge a response protocol is triggered.
Monitoring network changes
There have been a few queries regarding this year’s recently introduced toxic algae monitoring network changes. The new monitoring network uses ‘indicator’ or ‘sentinel’ sites to assess toxic algae risk, rather than results from all sites. Those problematic sites with a long history of toxic algal blooms were chosen as indicator (tier 1) sites. Tier 2 sites, are sites that are only assessed when tier 1 (indicator sites) exceed a certain threshold. Historically tier 2 sites have very rarely had toxic algae problems and when they have had issues it has only been when tier 1 sites have exceeded guideline levels. Sites, such as Tauherenikau River at Bucks Road, that have never had a toxic algae issue were dropped.
· Tier two sites are only monitored once an indicator (tier 1) sites exceeds a 15% threshold; thus, there will not always be results for these sites.
· Not all E. coli sites on the ‘is it safe to swim?’ web-page are monitored for toxic algae i.e. Tauherenikau River at Bucks Road.
· The Hutt River 500m upriver of Silverstream Bridge, a key indicator site, has not yet been added to the website but will be.