To start with our Indian Runner Ducks polluted the lake and ate the new shoots off the waterlilies before we could establish a nitrogen balance. Once we re-homed our ducks to the pond on the farm, they were no longer an issue, but then the wild Mallards found a new home and continued to graze on the flora in our lake, and added their own nitrogen to the water...
So at great expense we drained the lake, cleaned it out, replaced the lilies and other oxygen creating plants, and refilled the lake, but alas further accidents ensued, and the lake required draining again.
This time we are determined to get it right (especially with our opening this Spring!).
The lake liner has been completely removed, the edge of the lake reveled, the bridge started, and soon it will all be put back and planted straight away with approximately 25% surface area of plants (which will grow quickly to the required 33% which is generally considered to be the minimum amount of surface water coverage to keep a lake clean and clear and to deal with the nitrogen balance).
Warning to those considering clearing a green lake or pond by dropping bales of pea straw into it - it doesn't work!
At the same time as our great remediation we will install a proper water oxygenating fountain. There are several on the market, but for our little lake this 1/2 HP model with 5 different fountain heads seems to fit the bill, especially with 1 head specifically designed to oxygenate lakes of volumes up to 25000 cubic metres of water.