ABSTRAKWaduk Ir. H. Djuanda merupakan waduk multi fungsi yang salah satunya adalah untuk kegiatan budidaya ikan. Adanya input pakan dari kegiatan budidaya dapat menyebabkan peningkatan bahan organik dan penurunan konsentrasi oksigen terlarut. Kegiatan budidaya ikan dalam karamba jaring apung (KJA) menyumbang bahan organik ke perairan yang laju dekomposisinya (k) (per hari) dipengaruhi oleh suhu perairan. Tujuan penelitian ini untuk mengetahui kedalaman hipoksia di lokasi karamba jaring apung untuk budidaya ikan di Waduk Ir. H. Djuanda dan pengaruh suhu terhadap besarnya laju dekomposisi bahan organik (k). Penelitian kondisi hipoksia dilakukan di Waduk Ir. H Djuanda dan selanjutnya pengamatan BOD untuk penentuan laju dekomposisi bahan organik di Laboratorium Balai Penelitian Pemulihan dan Konservasi Sumberdaya Ikan pada bulan Februari-April 2013. Penentuan kondisi hipoksia berdasaran Peraturan Pemerintah Republik Indonesia Nomor 82 Tahun 2001 dan penentuan laju dekomposisi berdasarkan Least Square Method. Hasil penelitian menunjukkan bahwa kedalaman hipoksia dimulai pada kedalaman 3 m dan laju dekomposisi bahan organik (k) tertinggi pada suhu 28,5°C yaitu sebesar 0,189/hari. KATA KUNCI: Laju dekomposisi, hipoksia, bahan organik, suhu, Waduk Ir. H. DjuandaABSTRACT Ir H. Djuanda Reservoir is a multi-purpose reservoirs, one of which is for fisheries culture activity. Feed inputs from aquaculture activities can lead to an increase in organic matter and a decrease in dissolved oxygen concentration. Cultivation of fish in floating cage net contributing organic material into waters which the rate of organic matter decomposition (k) (per day) is affected by water temperature. The purpose of this study was to know the depth of hypoxia in floating cage net for fisheries culture in the Ir. H. Djuanda Reservoir and the effect of temperature on the amount of organic matter decomposition rates (k). Observation of hypoxic conditions was conducted in Ir. H Djuanda Reservoir and furthermore observation of BOD to determine the rate of organic matter decomposition at Research Institute for Rehabilitation and Conservation of Fish Resources laboratory in February-April, 2013. Determination of hypoxic conditions based on Government Regulation of the Republic Indonesia Number 81 Year 2001 and the determination of the rate of decomposition based on Least SquareMethod. The results showed that the depth of hypoxia began at a depth of 3 m and the higher of decomposition rate of organic matter (k) was 0.189/day at temperature 28.5°C.