In the provisions of the water law, in the section on amateur fishing, we find the term: open waters. We count among them, with the exception of breeding ponds and fishing waters, all types of water, regardless of whether they are natural or not, or are caused by human activity. (There are slightly different legal regulations in Poland: the conditions of amateur fishing in inland surface waters are regulated by the act of 18 IV 1985 r. about inland fisheries). Taking into account their basic hydrological properties, open waters are divided into:
– flowing waters (paths);
– standing waters.
Basic characteristics of flowing waters
The living conditions of fish in flowing waters are the resultant of the entire set of factors characterizing a given course: decline and flow ratios, formation of the placenta, shaping of the shores, vertical and horizontal shape of the trough, the nature and arrangement of the fundus, climatic conditions, physical and chemical properties of water, type of water and coastal vegetation, etc.. Considerable differences between individual watercourse sectors make it necessary to classify these waters according to typical sections, characterized by a clear and specific layout of the fish community, while taking into account the requirements of water management.(In fishing practice, the division of watercourses according to the so-called. fish lands (the author of this division in Poland is prof. F. Staff). The starting point is to identify the characteristics of a given environment and these characteristics of fish, thanks to which their specific species have objective predispositions to inhabit this type of environment. According to the above criteria, four basic ones can be distinguished among the flowing waters, sovereign to some extent, land: the land of trout, the land of grayling, the land of barbel and the land of bream. Of course, the essence of a given land does not have to come down to the presence of this species of fish, from which it takes its name. The ideal situation is then, when the land is marked by both basic determinants, tj. when its character corresponds to the predominant component of the fish stock. It often happens, that the type of fish stock is only partially consistent with the nature of the land, sometimes there is not even such a match. Relatively often such cases take place in the land of trout, from which "title”trout, despite the favorable conditions for it, have displaced other species, less typical of an environment of this nature. Sometimes the same happens with grayling – in some river basins there are sections that objectively meet the conditions of their land, but grayling does not occur in them. Individual lands should naturally adjoin each other, however, the boundaries between them are mostly blurred, a transition, one into the other, gradual.
Diagram of the division of the watercourse into four basic fish lands (the land of trout, grayling, barbels, bream). Animal and plant organisms typical of these lands:
A – spa sprout (Gammaruspulex),
B – bloodworm larva (Chironomus spec.).
C – monkfish larvae (Chloroperla spec.),
D - Common Mayfly larva (The New ephemera),
E-larva of shiny mantle (Calopteryx splen-dens),
F - Angler larva – (Aeschna),
G – flower larvae (Trichoptera),
H – daphnia (Daphnia),
And - eyelet(Cyclops),
J – buzzing mosquito larvae (Culex pipiens),
K – float larva yellow margin (Dytiscus marginalis),
L — common hen (Asellusaqua-purist),
M - puddle (Hydrouspiceus),
N – Canadian marsh (Elodea canadensis),
O - watercress (Nastartium job-nate),
P - moss sources (Fontinalis antipyretica),
R – marsh duckweed (Callitriche nail-tris),
S – buttercup (A floating frog),
T - shimmering knotweed (Potamoge-ton shining),
U – floating knotweed (Potamoge-ton swimming),
V - stiff toll-gate (Ceratophyllum drowned),
X - yellow water lily (Nuphar luteum),
Y - wywłócznik (Myriophyllum spec.)
In these cases, one should speak of mixed lands, transitional (often e.g.. Grayling is also present in the lands of trout or barbel). Several lands can be distinguished in larger streams, sometimes all of them, on smaller watercourses, however, we will observe only one or two. We are dealing with coincidences quite commonly, when the land of trout directly borders on the barbel belt, without the land of grayling between them.
In a specific way, deviating from natural rules, the fish lands of the watercourses are formed, on which larger hydrotechnical structures were erected, tanks in particular; sometimes irregularities are the result of regulating the watercourse.
The most noticeable changes occur as a result of the construction of dam reservoirs on piedmont rivers, the impacts are two-way: up the watercourse and down.
In the former case, the creation of a reservoir may significantly change the upper parts of the watercourse, and the original land of trout may become the land of grayling, and even – in extreme cases – the land of barbel. Looking at this phenomenon in terms of the qualitative composition of the fish stock, it must be considered negative, sometimes only counterbalanced by an increase in the number of fish. On the other hand, the changes downstream may be positive, because they bring an overall improvement in breeding conditions – they have a direct impact on a significant improvement in water quality (beneficial for fish change of its physical and chemical properties). However, the degree of the desired impact depends on the type of use and the hydrological regime of the watercourse, that is, practically on the flow rate. With periodic use of the tank (draining the water) improving the water quality does little, because the effect is wasted by a very varied amount of flow. In cases of extreme fluctuations in flow, the breeding value of the watercourse is very variable, sometimes it may be minimal.
Watercourse regulations, which boil down to the absolute straightening of the channel and transforming it into a concreted or stone-paved channel in practice mean severe (np. in Slovakia it affected the Nitra River, whose land of trout turned into the land of grayling), and sometimes complete destruction of the economic value of the watercourse.