**6.1 Reference conditions for rivers**

Although past data for rivers in Prespa Lake watershed are very scarce, the *reference conditions* were more or less easy to determine due to: a) all rivers belong to the same river type; b) they have very short and rapid flows prior to inflow in Prespa Lake; c) their source waters belong to two different parks of nature where they are significantly protected from any important human activities; d) even with a limited number of samplings, water chemistry and biology were easily distinguished from the rest of the river water courses where human impact was much more severe.

Therefore, a relatively solid starting proposal for the reference conditions of rivers in Prespa Lake watershed would be very close to conditions found in water bodies Kranska 1 and Brajčinska 1, which are: natural water courses with good hydraulic contact with surroundings, rich riparian vegetation, clear water with very low conductivity (<100), slightly acidic, low in nutrients which are easily biodegradable, and with variable natural flora and fauna in and around the water courses (Tab. 9).

natural discontinuous belt around the lake comprised of numerous dense complexes. Other representatives of emergent vegetation were present in the belt of reed and in particular localities, where they formed almost pure associations. *Phalaris arundinacea*, *Typha latifolia*, *Typha angustifilia* were present with a density of 2, while *Shoenoplectus lacustris*, *Scirpus sylvaticus*, *Heleocharis pallustris* and *Cyperus longus* were present with a density of 1. Nevertheless, to obtain detailed information about changes in composition and spatial disposition of the vegetation, aquatic and marsh vegetation, long-term investigations are

The fish population of the Prespa Lake is composed of 23 species of which 11 are autochthonous: *Alburnoides prespensis, Alburnus belvica, Anguilla anguilla, Barbus prespensis, Chondrostoma prespense, Cobitis meridionalis, Cyprinis carpio, Pelasgus prespensis, Rutilus* 

In the previous period 12 allochthonous species were introduced in Lake Prespa: *Carassius gibelio, Ctenopharyngodon idella, Gambusia holbrooki, Hypophthalmichthys molitrix, Lepomis gibbosus, Oncorhynchus mykiss, Parabramis pekinensis, Pseudorasbora parva, Rhodeus amarus,* 

*Alburnus belvica* and *Rutilus prespensis* were caught in the greatest number of specimens at all investigated localities from Lake Prespa. On the contrary, *Anguilla anguilla*, *Chondrostoma prespense*, *Cobitis meridionalis*, *Pelasgus prespensis* and *Salmo peristericus* were not caught at any of investigated localities. Also, in the catches from all investigated localities *Cyprinis* 

Populations of some of the introduced species are so reduced that they are very rarely present in representative and experimental fishing, like *Ctenopharyngodon idella*, *Hypophthalmichthys molitrix*, *Oncorhynchus mykiss*, *Parabramis pekinensis*, *Salmo letnica*, *Silurus glanis* and *Tinca tinca*. Others like *Carassius gibelio*, *Gambusia holbrooki*, *Lepomis gibbosus*, *Pseudorasbora parva* and *Rhodeus amarus* are present in the catches but in very low numbers.

Although past data for rivers in Prespa Lake watershed are very scarce, the *reference conditions* were more or less easy to determine due to: a) all rivers belong to the same river type; b) they have very short and rapid flows prior to inflow in Prespa Lake; c) their source waters belong to two different parks of nature where they are significantly protected from any important human activities; d) even with a limited number of samplings, water chemistry and biology were easily distinguished from the rest of the river water courses

Therefore, a relatively solid starting proposal for the reference conditions of rivers in Prespa Lake watershed would be very close to conditions found in water bodies Kranska 1 and Brajčinska 1, which are: natural water courses with good hydraulic contact with surroundings, rich riparian vegetation, clear water with very low conductivity (<100), slightly acidic, low in nutrients which are easily biodegradable, and with variable natural

*prespensis, Salmo peristericus* and *Squalius prespensis*.

*Salmo letnica, Silurus glanis* and *Tinca tinca*.

*carpio* was present, but in very low numbers.

**6. Reference conditions** 

**6.1 Reference conditions for rivers** 

where human impact was much more severe.

flora and fauna in and around the water courses (Tab. 9).

needed.


Table 9. Reference conditions for rivers in Prespa lake watershed.
