Aquatic biotopes are, due to their features, among the most disposed ecosystems to bioinvasion. Serbia waters are not an exception, with and increasing colonization by allochthnous organisms observed there during the last few decades. Non-indigenous aquatic species were found among plants, vertebrates and invertebrates. The aim of this work is to present the current status of aquatic ecosystems in Serbia in regard to biological invansions and to point up to the problem of introduction, presence and influence of aquatic non-indigenous species.

Due to very high concentration of organic matter there is a great need for alternative solutions for drinking water disinfection in the world. Chlorine dioxide has been successfully used for almost 50 years for disinfection and later for taste removal, odor control, color reduction and oxidation of inorganic compounds such as iron and manganese. An advantage of using chlorine dioxide instead of chlorine is that it does not directly react with organic matter and form halogenated byproducts when it is used for disinfection. THMs, such as CHBr3, ChCl3 etc, are considered as most dangerous for people health. In this article we are to represent the results got from raw water disinfection treatment with chlorine dioxide.

Coagulation and flocculation can be efficiency applied in drinkling water treatment, in order to remove natural organic matter (NOM). However, in the experiments presented in this paper, the water used is very rich in NOM, and required investigations of additional processes. In order to increase the efficiency of coagulation and flocculation processes in removing NOM from groundwater, the following processes were investigated: adsorption on powdered activated carbon (5-30 mg PAC/l) and preozonation with applied ozone doses of 1.1-6.3 mg O3/l. The parameters used to evaluated the changes in NOM content during the experiment were: KMnO4 consumption, UV absorbance at 254 nm, pH and turbidity.

One of the last stages in purification of waste water is by aquaculture pond using macro biological cells - fishes. In such outdoor ponds, oxygen depletion events can occur at anytime, but most likely to cause fish kills during summer hot weather. Aquaculture pond model can predict dissolved oxygen using small number of measurements and very simple numerical model. Alarm system can be activated urgently when the oxygen level drops below a certain concentration, depending on fish species. Such a model is realized for WWTP at Citluk coal mine, close to Sokobanja in Serbia, and explained in this paper.

The length - weight relationship of juvenile anchovy, Engraulis encrasicolus at Bokakotorska Bay (Adriatic sea, Montenegro) was analyzed. The better knowledge of juvenile growth needs more attention for the entire Adriatic, especial for the Montenegrin coast were this investigation made for the first time. The results obtained from this investigation were compared with the data obtained from the period 1989-1991 from the area of Novigrad Sea of the the eastern Adriatic coast (5).

In the beginning of 2008, on the Montenegrin coast is confirmed finding of new species, what was unknown until now in this part of Adriatic sea. The Sphoeroides cutaneus is tropical species with habitat in warm sea around Japan, China and Indonesia. Probably is one of the Lessepsian migrant. It tooks around 130 years for a fish to come through Suez Canal and Red Sea to Mediterranean, then through Otrant Strait into Adriatic sea. It is possible, also that this apparition has something with the global climate change and temperature rise in saltwater in Mediterranean as well as in Adriatic.

The red algae Womersleyella setacea is Indo-Pacific species but introduced to Mediterranean Sea were is now relatively widely distributed. During research of benthic communities in Ponta Veslo locality (Lusnica peninsula, Montenegrian coast, Adriatic sea) in summer 2007 dense assemblages on rocky substratum and on sea grass Posidonia oceanica (L.) Del. rhizomes were discovered. The impact on biocenosis structure is discussed.