Parallelogram? Trapezium? Rectangle? Pythagoras!

Dutchman measures the layout and dimensions of the new pond. It appears the old pond was a trapezium, a parallelogram and definitely not the rectangle it was supposed to be. The guys who built it out of hand sure didn't pay notice when Pythagoras was mentioned at school..
Anyway, as all the sight lines take the pond as a basis everything in the garden is askew. Dutchoak asks himself whether to build a non rectangular pond or shift the whole garden 30cm to the right...