Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. In spring, we can witness dramatic moments in the life cycles of many underwater creatures.

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. Here we see many animals emerge from hibernation, and then catch a glimpse of what lies over one hundred meters below the surface.

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. From the swiftly flowing streams to the cliffs high above, the area around the lakes hosts a number of different species.

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. In this episode, we'll explore the mysterious "Lake of Blood" and some scandalous interspecies dating!

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. In this part, we explore the mysterious "cow tracks" found throughout the Alps in stone. These are, in fact, ancient fossils from the time when this mountain range was an ocean floor.

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. Here we see the female perch defending her spawn from North American crayfish, and look at the role of glaciers in storing Alpine water.

Alpenseen (Alpine Lakes) is a nature documentary that shows us the fascinating world of deep mountain lakes. Here we see the effects of global warming, from the melting ice on the mountains to the caves of Slovenia.

Alpine Lakes, a nature documentary, leads us into the fascinating world of deep mountain lakes. As snow covers the mountains, mammals and fish alike fight for survival.

Alpine Lakes, a nature documentary, leads us into the fascinating world of deep mountain lakes. When winter comes and the lakes freeze over, the fish under the thick ice cover have different ways of passing the time.

The North Sea is an unpredictable and mysterious marine habitat, teeming with life. Join marine biologists Florian Graner and Natali Tesche-Ricciardi on an exciting adventure!

Florian and Natali finish a great first dive with the basking sharks and then make their way to the coast of Holland.

Toasting your friends and setting off fireworks is an essential part of the New Year celebration, but unfortunately the animals in the Berlin Zoo don't feel the same way! See how the Berlin Zoo tries to deal with the problems of inner-city fireworks and their animals. (video copyright dpa)

Florian and Natali join divers Joop and Felicia Stahlenburg in making underwater willow tipis for the endangered cuttlefish to spawn in.

In this installment, the sea creatures in the Oosterschelde are busy spawning and the male cuttlefish prepare for mating battle.

Now Florian and Natali leave behind the Oosterschelde and take to the air! In this episode, we get a glimpse of the mud flats in the intertidal zone: home to friendly seals and a resting place for migratory birds.