Artificial rapid – a fortified section of a mountain stream or channel with a steep gradient, designed to slow the flow of water and reduce its destructive force.
B
Bed load – material on the riverbed, such as sand, gravel or stones, moved by the water.
Bottom erosion – the process in which a river deepens its bed and valley, 'pulling' material from the bottom, mainly in the upper reaches of the river, where the current is fastest, and in sections straightened by river regulation.
Breeding colouration – the colouring that fish take on during the spawning season.
D
Delta –a wide, branching estuary where a river flows into the sea or a lake, formed by the deposition of sediment carried by the river and shaped by water currents.
E
Eutrophication – the over-fertilisation of water with nutrients that causes massive growth of plants and algae and disrupts the balance of the aquatic ecosystem; this is caused by fertiliser runoff from fields or by inadequately treated or untreated domestic sewage.
F
Fish larva – the stage lasting from hatching until the fish reaches its adult form.
Fish passage – a special structure at dams and weirs that allows fish to migrate upstream.
Fish-stocking material – eggs and juvenile fish (ranging from newly hatched to around two years old) intended for release into rivers and lakes or for further rearing in ponds.
Fluvial erosion – the action of a river that involves the undermining of banks and the deepening of the riverbed; a channel-forming process.
H
Homing – the ability of fish and other organisms to return to the same place where they reproduce.
K
Kelt – salmon or sea trout that return to the sea after spawning in the river.
L
Lateral erosion – the gradual scouring and breaking of river banks by flowing water, particularly evident where the river flows wide and meanders.
Lithophilous – fish that require gravel or stones for spawning.
N
Nest – fish such as Atlantic salmon and sea trout dig a structure into the gravelly riverbed in which the eggs are incubated.
O
Oxbow lake – a former bend in a river that has been cut off from the main channel and often forms calm bodies of water. They are formed as a result of natural processes or human activity.
P
Parr – the developmental stage of salmon from fry to the smoltification process.
Phytophilous – fish that spawn on plants.
R
Renaturalisation – restoring rivers to a state close to their natural condition. Currently, as many as 91% of Polish rivers require re-naturalisation.
Riffle – a section of a river where the water flows faster, churns and swirls, creating a distinctive, dynamic current.
River basin – an area of land from which surface water flows into a single river, which eventually reaches the sea.
S
Sexual dimorphism – differences in body structure resulting from the sex of the fish. This is particularly evident in salmonids, and not only during the spawning season.
Smolt – a salmon aged 2–5 years that migrates to the sea. During this period, changes occur in the fish’s body that enable it to live in salt water.
Spawner – an adult fish ready to breed.
Spawning ground – a place where fish lay their eggs and reproduce.
Spawning – the period and process during which fish reproduce, involving the fertilisation of eggs.
Stocking – releasing fish into rivers and lakes to replenish their numbers and protect endangered species.
Stream pool – a stretch of river with deep, calm water.
Substrate (spawning substrate) – the material that makes up the riverbed in the section of the river where fish spawn.
T
Turbine – a key component of a hydroelectric power station, a device that converts the energy of flowing water into the energy needed to generate electricity.
W
Water erosion – the general destruction of the earth's surface by runoff or flowing water.
