Years ago when I designed the garden we incorporated a bath as a water feature. It was positioned so that the fountain could be seen from inside the house at the end of a long passageway. All progressed very well but during the drought adding water to the bath was a low priority and the additional heat turned the water a lovely shade of green.
What to do? We did construct a shade frame for it but it took away from its original look then the tree frogs took over and laid so many eggs we had to turn off the fountain for a while.
One day it came to me that I needed a different way of shading the water while still having the bath act as a reservoir for the fountain so I could have the sound of water. I drained out the water gave the bath a good clean then added some stacks of brick to support a thick galvanized wire mesh and covered the top with small rocks. These rocks are from the garden and keep up turning up in the vegetable garden.