The Timok River (202 km long, 4547 km2 basin area) is located in East Serbia. It is a right tributary of the Danube River and one of the most polluted watercourses in Serbia. On the basis of the data provided by the Republic Hydrometeorological Service of Serbia, the paper presents an analysis of water quality and pollution using the combined physico-chemical WPI index (Water Pollution Index) calculated for two periods - 1993-96 and 2006-2009 at four hydrological stations: Zaječar-Gamzigrad (Crni Timok River), Zaječar (Beli Timok River), Rgotina (Borska Reka River) and Čokonjar (Timok River). The following parameters were taken into consideration: dissolved O2, O2 saturation, pH, suspended sediments, Five Day Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (CODMn), nitrites, nitrates, orthophosphates, ammonium, metals (Cu, Fe, Mn, Hg, Ni, Zn, Cd), sulphates and coliform germs. The average WPI values were calculated for the observed periods based on the comparison of the annual average values of the listed parameters and defined standard values for the I water quality class (according to the Regulation on the Hygienic Acceptability of Potable Water of the Republic of Serbia). The highest pollution degree was recorded in the Borska Reka River, where heavy metal levels (especially manganese and iron) were significantly increased. These metals are indicators of inorganic pollution (primarily caused by copper mining). Also, increased values of the organic pollution indicators (ammonium, coliform germs, Five-Day Biological Oxygen Demand - BOD5) in the Borska Reka and the Timok rivers are the result of uncontrolled domestic wastewater discharge.

Aluminium slag waste is a residue from aluminium recycling activities, classified as hazardous waste so its disposal into the environment without processing can cause environmental problems, including groundwater pollution. There are 90 illegal dumping areas for aluminium slag waste spread in the Sumobito District, Jombang Regency. This study aims to evaluate the quality of shallow groundwater surrounding aluminium slag disposal in the Sumobito District for drinking water. The methods applied an integrated water quality index ( WQI) and heavy metal pollution index ( HPI), multivariate analysis (principal component analysis (PCA) and hierarchical clustering analysis (HCA)), and geospatial analysis for assessing groundwater quality. The field campaign conducted 40 groundwater samples of the dug wells for measuring the groundwater level and 30 of them were analysed for the chemical contents. The results showed that some locations exceeded the quality standards for total dissolved solids ( TDS), electrical conductivity (EC), and Al ²⁺. The WQI shows that 7% of dug well samples are in poor drinking water condition, 73% are in good condition, and 20% are in excellent condition. The level of heavy metal contamination based on HPI is below the standard limit, but 13.3% of the water samples are classified as high contamination. The multivariate analysis shows that anthropogenic factors and natural sources/geogenic factors contributed to shallow groundwater quality in the study area. The geospatial map shows that the distribution of poor groundwater quality is in the northern area, following the direction of groundwater flow, and is a downstream area of aluminium slag waste contaminants.

This study aims to assess the water quality and determine the pollution index of the Bedadung River in the urban-area segment of Jember Regency, East Java. The sampling in the urban segment of Jember was conducted in May 2019 at five different locations, namely Slamet Riyadi Street, Mastrip Street, Bengawan Solo Street, Sumatra Street, and Imam Bonjol Street. The pollution index assessment refers to the Decree of the State Minister for the Environment of Indonesia Republic number 115 of 2003. The analysis showed that the parameters of TDS, TSS, pH, COD, BOD, NH3-N, Co, Cd, Cu, Zn, H2S, Cl–, SO4, oil and fats, MBAS, NO2-N, Fe, Pb, F, Cl2, NO3-N, phenol, and As did not exceed the quality standards. The parameters PO4, CN, total coliform, and faecal coliform were found to breach the quality standards at the 5 water sam-pling points. Total coliform and faecal coliform were the dominant pollutants in this segment. Therefore, the parameters of PO4, total coliform, and faecal coliform were considered as indicators of pollution arising from domestic and agricultural activities. The pollution index values for the five sampling locations ranged from 7.21 to 8.23. These scores indicate that the Bedadung River section that passes through the urban segment in Jember is classified as being in the moderately pollut-ed category. This preliminary rapid assessment is therefore one of the considerations for the management of water quality in the Bedadung River section that passes through the urban area of Jember.

Warna and Pengilon Lakes are very close to each other and connected with the sill, a famous tourist destination in the Dieng Plateau Java. Land-use changes are the main problem that affected the lakes. The conversion of forest into an agricultural area had induced erosion and increased the volume of nutrients discharged to the lake due to high use of fertilisers in potatoes farms. In the dry seasons, water from those lakes was pumped to irrigate agricultural land. This study aimed to determine the water quality of Warna and Pengilon Lakes based on physical, chemical parameters, and phytoplankton communities. Water samples were collected from 4 sites at each lake to analyse biological oxygen demand ( BOD), chemical oxygen demand ( COD), ammonia, nitrate, nitrite, and total nitrogen ( TN). Temperature, pH, dissolved oxygen ( DO), turbidity, and conductivity ( EC) were measured in-situ. During this research, turbidity and BOD in Warna and Pengilon Lakes exceeded the Indonesian water quality standard. Based on the STORET method, the water quality of Lake Warna was assessed as highly polluted for all classes. However, based on the pollution index (PI), Lake Warna was slightly to moderately polluted, as well as the saprobic index was in the β-mesosaprobic phase. Based on the species diversity index of phytoplankton, both Warna and Pengilon Lakes were moderately polluted. The long-term monitoring studies are necessary as an early warning sign of water quality degradation. Therefore, they provide insight into the overall ecological condition of the lake and can be used as a basis for developing suitable lake management.