Whale or dolphin?

No, this was neither a whale nor a dolphin splashing back into the water.
What you see here is one of the three ventilation systems in the Reinheimer Teich. This nature reserve was suffering significantly from the drought last year. Hence the local fire brigade installed three ventilation systems. A big power generator provides the systems with electricity (the reserve, inherently, has no "power" at all).
The drought this year was again causing problems for the reserve so the ventilators are running again.
No, there is no climate change, all fake news.