duck weed in a blocked natutral spring
I have a spring at the bottom of my garden ,that runs eventually into the River Thames some many miles away.
Duckweed I know does not like running water but the problem is that the free flow on the top is impeded by leaves,weeds etc.also possibly by neighbours not clearing the surface
I can clear it and for a while and it washes downstream, but wondered whether perhaps excluding light with a tarp/poly etc over the surface, about a metre wide max . might eventually kill it in situ. as the dw multiplies at an astounding rate.
I have heard that freshwater carp eat the stuff but it is not legal to introduce,even if I knew where to obtain some.
As far as I am aware no weedkiller is allowed to be used?