It’s early morning, a view from the air shows the Biebrza river's water reflecting the blue sky as the sun rises. The river’s outline stands out in the flooded valley. The river looks wild and winding. A huge flock of geese lands on the water surface. They are nervous - a young sea eagle is patrolling the area. When it flies over the geese, the whole group escapes terrified. However, the large predator is not interested in them – the melting snow has revealed a dead fox. Several eagles are already competing to feed on the carcass. While one of them is eating, a number of crows work together to distract it and access the meat. But the eagle is hungry and scares the crows away. Geese are eating in a rush – they only have a few days before they continue their journey. One day, at sunrise, the flock of thousands of geese takes off from the marshes towards their next destination.
In the marshes of an alder forest, spring begins. Tree contours from underwater look like a surreal drawing. Silhouettes of swimming moor frogs block the view. On the water surface, a big number of blue-colored males are croaking – they have just begun their mating season. Any female that appears is immediately caught by an excited male. The water is soon full of spawn. In the same marshes, newts perform their nuptial dance. The brightly colored male swims around the female and moves his tale to impress her. He is very subtle and seems fully in love with the female. A grass snake is gazing at the group of moor frogs, ready to attack. From the other side of the marshes, a white stork walks carefully in the water in search of prey. Finally, the snake swims towards the frogs. At the same time, the stork makes an attempt to attack a frog but fails. The grass snake swimming amongst a large number of frogs had clearly miscalculated his chances – the excited male moor frogs, instead of being an easy catch, attack the snake, forcing him to escape. The white stork, however, is a merciless killer – it suddenly catches a frog and brutally devours it.
From the air one can notice that spring is slowly coming on the Biebrza valley. Here and there fresh green grass can be seen. For many birds, it’s mating season while a huge flock of ruffs on their migration route arrives in the river valley. They are intensely feeding. Bluethroats and several other birds are singing nearby, amongst fresh green leaves of willows and on the marshes ground. A love call of cranes comes from a distance. In marshes surrounded by a flooded alder forest, a pair of cranes are dancing their nuptial dance. Bluethroats are singing nearby, amongst fresh green leaves of willows.
In the underwater marshes, in a transparent egg, a tadpole gets ready to hatch and eventually comes out. Tadpoles hatch in huge numbers. Several predators have long been waiting for this moment. Even a river snail is taking advantage of the easy situation and feeding on the still motionless tadpoles. A diving bell spider is building his underwater tent filled with air. With his abdomen inside the tent, he waits upside down for prey to pass. A newly hatched frog is an easy catch for him. Nearby, an alien-like larva of a great diving beetle catches tadpoles effortlessly. At the bottom, tadpole shrimps are feeding on the remaining. With their brown armor and simple eyes, they look very primitive – they haven’t changed for over 200 million years. In the motionless water of these marshes full of dragonflies, mayfly, caddisfly larvae, and hundreds of other small animals, predators aren’t safe either. Tadpole shrimp carcasses are eventually being eaten by a snail and even moor frog tadpoles. Above the water, a big animal is walking in the forest marshes – it is an elk, feeding on the fresh leaves of a tree, unaware of the underwater life.
The riverbank is a yellow carpet of blossoming kingcups. A flock of white-winged terns is flying over the flowers and patrolling the area, eventually hunting small fish. As a nuptial gift, a male brings a small fish to a female. In a flooded alder forest, a crane is sitting on its nest. Not far pool frogs are mating, their croaking is louder than any other sound.
In the Lawki marshes, a female elk with her young is grazing. The grass is covered with dew, thousands of spider webs are flowing in the wind. Among the grass, an aquatic warbler is singing. A huge thunderstorm interferes with the valley forcing a group of a white stork to stop their activity and wait for the rain to stop. After the storm on the nearby meadows, several clouded apollo butterflies are flying around searching for a partner. When a male finds a female he immediately approaches her. Young foxes play near their den. Spring is happiness and joy. Sometimes, however, a butterfly ends in a spider web, where the host doesn't show mercy.
Swimming underwater in the river Biebrza. Long branches of beautiful aquatic plants are slowly fluctuating, moved by the river current. A group of fish is swimming near the bottom, collecting organic matter. An impressive amount of fish is swimming between aquatic plants and freshwater sponges, a northern pike is gazing at them. A group of amur bitterlings swims around a mussel: a male bitterling with the nuptial coloration is scaring away every other fish that swims close by. Every fish apart from a female with a long ovipositor developed under the stomach. She and her partner are moving closer and closer to the mussel. Finally, the female puts her ovipositor inside an opening of the mussel and lays an egg. But the mussel throws the egg out, far away.
At sunrise, in a meadow full of yellow kingcups, several white herons have just started to hunt. The sky is full of sterns and small groups of ruffs are landing here and there. A grayed goose emerges from the tall green grass. Herons are now deeply involved in the hunt. The sinuous movement of their neck is almost hypnotic. An adult finally captures a huge European weatherfish – the fish does its best to escape the mortal bill but the heron is stronger and finally swallows it. As the heron takes off from the hunting ground, the camera is also flying over the river valley. Everything around is green, a green sea of marsh grass crossed by the blue winding course of the river. The white heron finally lands on its nest were four hungry nestlings are waiting for him. They loudly ask the parents for food and finally get fed.
The sun rises over the river valley overwhelmed by fog. A group of white storks has just gathered in the meadows, frantically feeding – it's their last lunch before the beginning of the long journey that will bring them to Africa. Not far away, in the marshes, a strange noise resounds – a huge elk come out of tall vegetation and calls loudly. It's the elks' mating season. Males are fighting to access the females. From a distance, the call of cranes rings out: thousands of them have woken up after a night spent in the marshes water. The cranes finally, take off and leave the river valley. Autumn has arrived at Biebrza, with its yellow and reddish colors.
The riverbank is frozen. An otter jumps out of the water and sits on the ice eating her catch, a frog. A beaver is walking on ice and dragging small branches. He reaches the water and swims away with a piece of wood. In the forest covered by snow an isolated wolf is moving around suspiciously. Nearby, some elks are feeding. In a heavy snowstorm, a young is eating small branches. Everything in the valley is covered with ice. The emptiness of the river landscape is enforced by the sad image of a sea eagle devouring a carcass of an elk.
Under the ice water plants are moved by the river current and small European weatherfish move around in the gradually melting ice. These are the first sign that winter is coming to an end. In the distance a loud call of a huge flock of geese echoes. They are returning to the Biebrza valley, the next cycle of river life begins.