Dirt in pond

In our part of Scotland we had four days of constant rain.
This made our raised pond quite dirty and murky.

It was just settling down again when I foolishly removed a Pepper grass
plant (by the grass, instead of grabbing the container) and silted it up
again !

Once again the pond starts to clear just fine.
However, this morning it's worse.

I've cleaned out the pump (Hozelock Titan 2000), the filter (Hozelock
EcoClear 2200UVC) is running OK and shows not enough "red" to need
cleaned.

The pond is 4'x3', 24'' deep,162 gallons, and is usually very clear (even
though there are two Shubunkins, two small Comets, two Golden Orfe fry, and
a very small Tench in residence...fear not the pond will be enlarged to cope
presently)

Unless my evil nephew has carried out his threat and dumped his two pond
loaches in without my knowledge ('cos I can't afford to buy his Ubertank...I
ask you, 400 gallons in a upstairs room ?? ), I don't know what's silting it
up ?

Peter