Abstract

Lak Lake (Dak Lak) plays an important role in regulating the flow of the Sêrêpôk River, providing domestic water, irrigation, and hydropower for the region. A study was conducted to assess the current water environment status through hydrochemical indicators in 2020, while also evaluating the lake's water quality variations during the period 2001-2020. Ten samples of water were collected in 2 seasons: rainy season August 2020 and dry season November 2020. The research results show that the water quality of Lak Lake in 2020 was poor due to low dissolved oxygen concentration. The DO parameter ranged from 3.76 to 5.07 mg/l, with an average of 4.42 mg/l across both seasons, which was  the level C of the QCVN 08:2023/BTNMT standard. In particular, DO level at HL-01 site was (3.76 mg/L) in accordance with standard D of QCVN 08: 2023/BTNMT. The average BOD₅ index of the lake was (1.50±0.81 mg/L) the level A of QCVN 08: 2023/BTNMT, except for HL-03 site in the dry season with BOD5 level was in  accordance with standard B of QCVN 08: 2023/BTNMT. The water quality of Lak Lake has also deteriorated over time, as parameters such as NO₃^-, PO₄^3-, BOD₅, and COD tend to increase, while DO tends to decrease. In that NO₃^- concentration in 2020 was higher 9.57 times than in 2006; The average PO₄^3-  concentration in 2020 was higher 1.86 times than in 2006; The COD index in 2009 was higher 1.9 times than in 2006 but the BOD₅ in 2009 was higher 3.1 times than 2001 and in 2020 was higher 1.68 times than in 2001. The dissolved oxygen content in water decreased from 6.6 mg/l in 2001 to 4.42 mg/l in 2020 (decrease 1.49 times).