We did a variation on this in science class as kids, which our teacher called a "slice of life". Basically you take two sheets of transparent nylon and bolt a

We did a variation on this in science class as kids, which our teacher called a "slice of life". Basically you take two sheets of transparent nylon and bolt a U-shaped rubber or nylon tube in between them such that the two sheets flex outwards in the middle in a pouch shape. Then you stand it up so that the opening faces up, and pour the water in. If it leaks, you might need to space the bolts closer together or add some sealant. And you'll probably also need to make some stands to go on either end and keep it upright. The curved nylon sheets act as lenses which magnify the pond life a bit - just be careful if you have pets.