Plants dying

I have had my pond up and running for about 4 months, we have koi, gold fish, blue orfe etc..

The problem we are having is that all the plants are dying below the water level !, they are fine above the water level.

The plants are parrots feather etc.

The water in the pond is not clear, it is green but has no floating algae, we have a good filter system a waterfall and fountain.

does anyone have any ideas, or is this normal

thanks
Colin

I have not had Parrots Feather for very long, but mine are doing the same. I think this is normal.

BTW, floating algae generally occurs when the water reaches a certain temperature, as it cools, the algae sinks back down.