Shorty :

That may be a big factor in all your plant growth. They even spread/ transport certain types of plants from pond to pond.

With most fert. including cows you can somewhat control what gets in the water directly. One danger is with a large influx (of ducks or geese) at one time you can have ammonia problems.


http://aquanic.org/publicat/usda_rac/efs/srac/463fs.pdf