Pertambangan Emas Tanpa Izin (PETI) di Kecamatan Nanga Mahap, Kabupaten Sekadau, masih berlangsung dan berpotensi menimbulkan pencemaran serta kerusakan lingkungan hidup, seperti penurunan kualitas air sungai, kerusakan tanah, terganggunya ekosistem, serta dampak terhadap kehidupan sosial ekonomi masyarakat. Padahal, Pemerintah Kabupaten Sekadau memiliki kewenangan melakukan penegakan hukum lingkungan sebagaimana diatur dalam Pasal 5 ayat (1) huruf p Peraturan Daerah Kabupaten Sekadau Nomor 3 Tahun 2015 tentang Perlindungan dan Pengelolaan Lingkungan Hidup. Namun, aktivitas PETI yang masih terus berlangsung menunjukkan bahwa penegakan hukum lingkungan belum dilaksanakan secara efektif. Penelitian ini menggunakan metode hukum empiris dengan pendekatan deskriptif kualitatif. Data diperoleh melalui wawancara, observasi, dokumentasi, kuesioner, dan studi kepustakaan, kemudian dianalisis secara kualitatif. Penelitian ini bertujuan menganalisis faktor-faktor yang menyebabkan penegakan hukum lingkungan akibat PETI berdasarkan Pasal 5 ayat (1) huruf p Peraturan Daerah Kabupaten Sekadau Nomor 3 Tahun 2015 belum dilaksanakan secara efektif, serta mengetahui upaya pemerintah daerah dalam penegakan hukum lingkungan akibat aktivitas PETI. Hasil penelitian menunjukkan bahwa penegakan hukum lingkungan akibat aktivitas PETI di Kecamatan Nanga Mahap khususnya di Desa Tembaga, Landau Apin, dan Batu Pahat belum dilaksanakan secara efektif. Kondisi tersebut dipengaruhi oleh beberapa faktor, yaitu faktor penegak hukum yang belum optimal, keterbatasan sarana dan prasarana, rendahnya kesadaran hukum masyarakat, faktor kebudayaan berupa ketergantungan masyarakat terhadap PETI sebagai sumber mata pencaharian. Upaya yang telah dilakukan pemerintah daerah bersama instansi terkait meliputi pengawasan, pemantauan kualitas lingkungan, razia, penertiban, penghentian aktivitas PETI, dan penyitaan mesin dompeng. Namun, upaya preventif berupa sosialisasi dan penyuluhan mengenai bahaya serta dampak PETI masih belum optimal sehingga belum mampu meningkatkan kesadaran hukum masyarakat secara maksimal. Oleh karena itu, diperlukan peningkatan koordinasi antarinstansi, penguatan pengawasan, optimalisasi sosialisasi dan pembinaan hukum kepada masyarakat, serta penyediaan alternatif mata pencaharian guna mendukung efektivitas penegakan hukum lingkungan dan mewujudkan kelestarian lingkungan hidup di Kecamatan Nanga Mahap, Kabupaten Sekadau. Kata Kunci: Penegakan Hukum Lingkungan, Pertambangan Emas Tanpa Izin (PETI), Lingkungan Hidup, Pemerintah Daerah Kabupaten Sekadau. Illegal Gold Mining (PETI) in Nanga Mahap District, Sekadau Regency, is still ongoing and has the potential to cause environmental pollution and damage, such as decreased river water quality, soil damage, ecosystem disruption, and impacts on the socio-economic life of the community. The Sekadau Regency Government has the authority to enforce environmental law, as stipulated in Article 5 paragraph (1) letter p of Sekadau Regency Regulation Number 3 of 2015 concerning Environmental Protection and Management. However, the ongoing PETI activities indicate that environmental law enforcement has not been implemented effectively. This study used an empirical legal method with a qualitative descriptive approach. Data were obtained through interviews, observations, documentation, questionnaires, and literature studies, then analyzed qualitatively. This study aims to analyze the factors that cause environmental law enforcement due to PETI, based on Article 5 paragraph (1) letter p of Sekadau Regency Regulation Number 3 of 2015, to not be implemented effectively, and to determine the local government's efforts to enforce environmental law due to PETI activities. The research results indicate that environmental law enforcement related to illegal mining (PETI) activities in Nanga Mahap District, particularly in Tembaga, Landau Apin, and Batu Pahat Villages, has not been effectively implemented. This situation is influenced by several factors, including suboptimal law enforcement, limited facilities and infrastructure, low public legal awareness, and cultural factors such as community dependence on PETI as a source of livelihood. Efforts undertaken by the local government and relevant agencies include supervision, environmental quality monitoring, raids, enforcement, cessation of PETI activities, and confiscation of mining machines. However, preventive efforts, such as outreach and education regarding the dangers and impacts of PETI, have not been optimal, thus failing to fully raise public legal awareness. Therefore, improved inter-agency coordination, strengthened oversight, optimized outreach and legal guidance for the community, and the provision of alternative livelihoods are needed to support effective environmental law enforcement and achieve environmental sustainability in Nanga Mahap District, Sekadau Regency. Keywords: Environmental Law Enforcement, Illegal Gold Mining (PETI), Environment, Local Government Sekadau Regency.