A possible barrier

[illusion54]

Do you think the gardening fabric that landscapers use to cover the dirt then add gravel onto the fabric to keep weeds out and the gravel from mixing with the dirt.

I'm thinking it would work, i just dont know if it contains any chemicals and such that would affect the water?

Example of Landscaping Fabric

 

[houndour]

your link doesnt go to the right page i think.

I dont see why it wouldn't be ok. The only thing I can thik of checking is maybe there might be some kind of persticide in the mesh, but I doubt it and surely it would tell you?

If you were concerned, you could use a finer fish pond net. I would imagine even with 1cm holes it would do the job?