A Water Bug

This little bug,possibly a water bug nymph, appeared on the surface of the water in a petri dish with water from the pond and duck weed . It is barely visible to the naked eye. Less than 1mm. It runs all over the surface of the water stopping to clean itself every now and again. It has a long, what looks like a sucking proboscis.At first I thought it was the water beetle but the larva is still there and very much bigger,7mm with other small ones now present.The pond is man made and there must be very few ponds occurring naturally in New Zealand like this one, so where does all this life come from? The pond though is 150 years old.