Punched steel (above) is the material imagined at the underside of the fish hatchery building.  A single sheet of material was held over various water sources to produce an effect based on certain times of day, water conditions, etc.

Image-1 above is daylight under cloudy conditions, little reflectance off the fish pond.

Image-2 above is daylight with evening light reflecting off the fish pond (Lake Merritt).

Image-3 above is light with noon light reflecting off the fish pond (Kroeber fountain).