The German Environmental Aid Association works towards and takes a strong stance on finding alternative methods of sustainable energies and environmentally compatible products. Get involved to help them here:
https://www.duh.de/spenden/

If you are interested in protecting nature conservation and want to see how you can be involved in more environment protection this could be the opportunity for you
https://www.dnr.de/

Greenpeace volunteers are always there when they suspect danger to the environment and protecting against various causes such as toxic pollution of the environment. If you want to join their cause see when and where
https://www.greenpeace.de/

The German Nature Conservation Association has been working on getting people excited about experiencing and appreciating nature through political action, education and projects to save nature.
https://www.nabu.de/spenden-und-mitmachen/index.html

Robin Wood is an environmental organisation fighting against forest dieback in Germany, also active in the fields of energy and traffic.
https://www.robinwood.de/aktivwerden