Dissolved oxygen concentration (DO), electrical conductivity (EC), temperature, pH and turbidity were measured in-situ with a YSI Professional Plus meter (YSI Inc., USA) and a portable turbimeter (Hach 2100P ISO, USA).Well-mixed water samples from the thalweg were immediately filtered through pre-weighed glass-fibre filters (Whatman GF/F, pre-combusted at 450 ◦C/4 h). Filtrate was transported in 500 ml PET bottles at 4 ◦C pending labanalysis within 8–48 h NH4–N and PO4–P were determined using United States Environmental Protection Agency Standard Methods (350.2 and 4500-P) and a Hitachi U-2000 spectrophotometer.