How to get clear, algea-free pond water with a natural gravel-filter-pond and solar-powered pumps.
More information here: http://www.pondtrademag.com/bog-gravel-filtration-water-cleaned-by-mother-nature/

 

Photos after construction in 2017, Location: Socodor, AR, Romania:

 

 

 

 

 

 

Update one year later (April 2018):
Our test pond has developed nicely, the water is quite nice and clear (thanks to the solar-powered pumps and the natural bog gravel filter), the aquatic plants have grown and are blooming, the fish (mainly american largemouth bass) are healthy, growing fast and reproducing. A pond/aquarium water test kit says all relevant water quality values are very good. The water plant that is covering a large part of the pond is: Potamogeton crispus. It's a natural local species here in Europe, but an invasive species in the U.S. We are actually very happy with this plant: it produces lots of oxygen, provides cover for fish, is easy to remove in case of need and most importantly: provides shade to the pond and absorbs lots of nutrients (phosphates, nitrates) - and therefore prevents algea growth very effectively. The plant survives winter/ice and lasts several years - but one should remove it before it eventually dies, because it will obviously re-release all absorbed nutrients back into the water when dying and decomposing.