In the fourth part of the Danube series, we follow the river on its last third. From the spectacular gorges of the Iron Gate, we go to the Danube Delta, a natural paradise, shortly before it flows into the Black Sea. At the Iron Gate, the Danube forces its way through narrow gorges with rock faces up to 300 metres high. At its narrowest point, the river is just 150 metres wide here. With its rapids and whirlpools, this section was considered the most dangerous of all. Only a large hydroelectric power plant with a dam completely changed the character of the Danube. Five kilometres before the dam, fisherman Duško Lazarević has cast his nets on the Serbian side - at one of the deepest points of the Danube. It is more than 50 m to the bottom. Dammed up by the dam. One fish in particular likes deep waters, the catfish. And hunting them is Duško's speciality. But first he has to lure it out of the depths - with a Bućka. Hunting pests Mosquitoes are the enemy of all Danube dwellers in summer. Georgi Georgiev is the saviour in their time of need. Every day, the Bulgarian mixes 500 litres of mosquito poison. With his car and a spray canon, he envelops the Bulgarian Danube bank in huge clouds of mist. Danube Delta - a natural paradise Shortly before it flows into the Black Sea, the Danube spreads out into countless arms. The Danube Delta. 5,000 square kilometres of natural landscape of lagoons, marshes and lakes, largely left to itself. Raluca Ilie is a nurse in the Danube Delta. Twice a week she has shift duty on the emergency boat. A fisherman slipped on his boat and broke his hand. Routine for Raluca and her floating hospital.