16-Jun-2006
- The Environment Agency officers worked against
the clock to save thousands of fish in Mansbridge
Reservoir at Southampton following a natural collapse
in water oxygen levels.
A member of the public alerted
the Environment Agency to the incident on Wednesday
14 June. Fish including carp, pike, rudd, roach,
tench, eels and perch were seen gasping at the
surface of the lake. The reservoir is an important
site for nature conservation as well as a free
public fishery.
When the officers arrived on
the scene they quickly saw that a very serious
incident was occurring with virtually every fish
in the lake at the surface fighting for life.
Oxygen readings and water samples lead the officers
to diagnose the problem as a phenomenon known
as an algal crash.
This occasionally occurs on
waters where a natural bloom of phytoplankton
suddenly can no longer support itself and dies
off. This then leads to a massive demand in available
oxygen as bacteria breaks down the decaying algae.
With the entire fish population
near death, the Environment Agencies Fisheries
team deployed an emergency procedure, which involved
pumping in large quantities of hydrogen peroxide.
The whole rescue operation took over 10 hours
to complete, and as a result the fish stocks have
been protected and a major fish kill was prevented.
Andy Thomas, Fisheries Technical
Specialist for Hampshire, said: "Mansbridge
Reservoir is normally very well balanced environmentally.
It seems that the abnormal weather patterns of
prolonged drought followed by wet weather, a week
of intense sunshine and then a cloudy dark day
has caused the algae to bloom and then die.
"We pumped in 420 litres
of hydrogen peroxide and monitored oxygen levels
until we were satisfied that the lake could recover
naturally. This is a very valuable conservation
area and is designated as a Site of Special Scientific
Interest. It provides a wonderful recreational
resource for the people of Southampton and we
are determined to do all we can to preserve it."
Mansbridge Reservoir is
owned and maintained by Southampton City Council.
Lucy Harding
