Lame Duckweed clearance for tourist barges on Lee Navigation
Around half of the water in the River Lea downstream of the Deephams sewage treatment works near Tottenham is treated sewage effluent. A significant proportion of the remainder is untreated sewage overflows from overburdened Victorian sewage treatment works and old illegal domestic sewage pipes discharging directly into the river. Much domestic 'grey water' also contains nutrients water plants like Duckweed can feed on.
When the hot summer sun returns to energise their growth processes these weeds rapidly colonise the slow moving waters of the Lee Navigation (canal) and the newly impound Old River Lee around the Olympic Park. The Canal and River Trust (until recently called British Waterways) have special weed clearance boats of various capabilities to skim and otherwise remove these blooms which can stifle a wider range of fish, smaller creatures and other plants by shading the sunlight below the surface.
The boat in this picture (9 Aug) is one which removes well the much larger leaved plants like Pennywort but is not suitable for the tiny free floating Duckweed. But this plant is currently growing so fast that someone decided it would be better to be seen doing something even if it is about as effective as catching snowflakes to stop it settling.
Submitted by Martin Slavin on Fri, 10/08/2012 - 20:39.