You're right....reduced by half ,in a way you're lucky ,here in some areas it's less 80% or even 90%.Frightening!!!hi,
in addition to all good reasons above there is the significant reduction of surface tension due to phosphats/nitrats.
the hatch is more difficult in such a weak surface>>a)turbo hatch in short time or b)a lot of emergents which will
be eaten subsurface.the investigations were done by switzerland,england and some benulux fishermen imho.
as long as this pollution together with the pharmaceutical and agriculture will not be reduced>>>nothing will change to better.