Pemantauan kualitas air sungai perlu dilakukan secara berkala untuk mengetahui kesesuaian air dengan peruntukkannya. salah satu cara menentukan status mutu air yaitu dengan menggunakan metode indeks pencemaran. indeks pencemaran dapat menilai tingkat pencemaran dan memberikan gambaran mengenai seberapa tercemarnya suatu perairan sungai. penelitian bertujuan untuk menentukan status mutu air menggunakan metode indeks pencemaran di sungai bengawan. penentuan status mutu mengacu pada peraturan menteri lingkungan hidup dan kehutanan nomor 27 tahun 2021 tentang indeks kualitas lingkungan hidup, sedangkan hasil pengukuran kualitas air dibandingkan dengan baku mutu peraturan pemerintah nomor 22 tahun 2021 pada lampiran vi tentang baku mutu air sungai dan sejenisnya, serta penentuan kelas air mengacu pada peraturan walikota tarakan nomor 04 tahun 2010 tercantum pada lampiran ii. pengambilan sampel dilakukan pada saat air surut sebanyak 5 stasiun atau 15 titik. parameter yang diukur yaitu tss, ph, do, bod, cod, nitrat dan fosfat. hasil pengukuran tss berkisar antara 15-50 mg/l, ph 5,98-6,34, do 4,8-7,2 mg/l, bod 0,3-6,4 mg/l, cod 16-64 mg/l, nitrat 0,35-1,18 mg/l dan fosfat 0,10-0,20 mg/l. hasil perhitungan indeks pencemaran berkisar antara 1,49-3,68, kemudian dikonversi ke dalam indeks kualitas air menjadi 50. nilai tersebut menunjukkan bahwa sungai bengawan masuk ke dalam kategori cemar ringan, sedangkan indeks kualitas air masuk ke dalam katagori kualitas air sedang. kata kunci: baku mutu air, indeks mutu air, kualitas air

Periodically monitoring river water quality is necessary to assess whether the water is suitable for its intended usage. the pollution index approach is one way to assess the state of the water quality. the pollution index can evaluate the degree of pollution and give a general picture of how contaminated the waters of a river are. the purpose of the study was to assess the bengawan river's water quality status using the pollution index method. determination of quality status referred to the regulation of the minister of environment and forestry number 27 of 2021 concerning the environmental quality index, while the results of water quality measurements were compared with the quality standards of government regulation number 22 of 2021 in appendix vi concerning river water quality standards and the like, and determination of water class referred to the regulation of the mayor of tarakan number 04 of 2010 listed in appendix ii. sampling was carried out at low tide at 5 stations or 15 points. the parameters measured were tss, ph, do, bod, cod, nitrate and phosphate. the results of tss measurements ranged from 15-50 mg/l, ph 5.98-6.34, do 4.8-7.2 mg/l, bod 0.3-6.4 mg/l, cod 16-64 mg/l, nitrate 0.35-1.18 mg/l and phosphate 0.10-0.20 mg/l. the results of the pollution index calculation ranged from 1.48-3.67, then converted into a water quality index of 50. this value indicates that the bengawan river is in the light pollution category, while the water quality index is in the moderate water quality category. keywords: water quality standard, water quality index, water quality