There are to variables that seem to drain the water in the pond:
1. High temperatures: Water levels could go down because of <em>evaporation</em> due to <em>high temperatures.</em>
2. Animals drinking water: Water levels could also go down because of the animals drinking water. However, <em>high temperatures</em> also affect this as they drink more water when it is warmer.
In conclusion, <em>high temperatures</em> are causing the water to go down.