Pulau Derawan tetap jadi destinasi populer di Kalimantan Timur, tetapi ekosistem pesisirnya, terutama terumbu karang dan lamun, sangat rentan. Penelitian ini ingin mengecek kualitas air laut dan daya dukung lingkungan di sekitar penginapan laut di Pulau Derawan. Sampel diambil di sebelas titik pantau, baik saat air pasang maupun surut. Parameter yang dianalisa antara lain suhu, salinitas, pH, kecerahan, oksigen terlarut (DO), total suspended solid (TSS), amonia, orto-fosfat, serta minyak dan lemak. Hasil penelitian menunjukkan TSS stabil di angka rendah 0,0115 mg/L, artinya sedimen dari aktivitas manusia sangat minim. Amonia sedikit lebih tinggi pada fase surut 0,0022-0,0023 mg/L, kemungkinan karena bahan organik yang terakumulasi, tetapi masih berada di bawah batas baku mutu. Fosfat tetap konsisten di 0,0011 mg/L dan sebagian besar berasal dari proses alami, sementara minyak dan lemak berfluktuasi antara 0,0002-0,0011 mg/L, dengan beberapa titik memiliki pengaruh dari aktivitas manusia. Indeks Kualitas Air Laut (IKAL) tercatat 81,16-95,93 persen, masuk kategori baik hingga sangat baik, dengan TSS sebagai penentu utama. Di sisi daya dukung, kapasitas asimilasi perairan masih memadai, walau pemantauan rutin pada fosfat dan amonia tetap penting untuk mencegah eutrofikasi dan penumpukan polutan organik.

Kata kunci : Hidrodinamika laut, ekowisata, sulu-sulawesi marine ecoregion, pencemaran domestik

Derawan Island remains a popular destination in East Kalimantan, but its coastal ecosystem, especially coral reefs and sea grass, are very vulnerable. The purpose of this study was to check the quality of seawater and the environmental carrying capacity around marine accommodation on Derawan Island. Samples were taken at eleven monitoring points, bith during high and low tide. The parameters analysed included temperature salinity, , brightness, dissolved oxygen (DO), total suspended solid (TSS), ammonia, orto-phoshate, and oil and fat. The results showed that TSS was stable at a low of 0,0115 mg/L, meaning that sediment from human activities was very minimal. Ammonia was slightly higher during the low tide phase at 0,0022-0,0023 mg/L, possibly due to accumulated organic water, but still below the quality standard limit. Phosphate remained consistent at 0.0011 mg/L and mostly came from natural processes, while oil and fat fluctuated between 0,0002-0,0011 mg/L, with some point having an influence from human activities. The Sea Water Quality Index (IKAL) was recorded at 81.16-95-.93 percent, categorized as good to very good, with TSS as the main determinant. In terms of carrying capacity, the assimilation capacity of the waters is still adequate, although routine monitoring of phosphate and ammonia remains important to prevent eutrophication and accumulation of organic pollutans Keywords : Marine Hydro-dynamics, Ecotourism, Sulu-Sulawesi Marine Ecoregion, Domestic Pollution