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
status
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.
Wellington
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.
Website
· 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.
ends