The Gwda is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Poland

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

.

It is 146 kilometers long and begins at Lake Studnica, northeast of Szczecinek

Szczecinek

Szczecinek [] is a city in Middle Pomerania, northwestern Poland with some 39,777 inhabitants . Previously in Koszalin Voivodeship , it has been the capital of Szczecinek County in the West Pomeranian Voivodeship since 1999...

. Its upper course flows through many lakes. It runs through the town of Piła.

Special fishing rules and regulations regarding trout

Trout

Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

are in effect for the following sections of the Gwda:

• Downstream from Koszalin Province boundary and upstream from road bridge in Ledyczek excluding reservoir between Wegorzewo and Lomczewo.
• Downstream from road bridge in Ledyczek and upstream from Podgaje Reservoir.
• Downstream from dam in Tarnowka and upstream from road bridge in Krepsko.

The water of the Gwda was one of the purest in Poland in 1975. However, the water flows have since been degraded due to cities pumping non-processed sewage and industrial plants flushing chemicals and oil.