The environmentally critical areas in the municipality under Presidential Proclamation No. 2146 are the NIPAS areas, timberlands, areas that are prone and vulnerable to natural hazards, areas with critical slopes, areas classified as prime agricultural lands and water bodies.

The Bulusan Volcano mountain ranges including Mt. Agoho and Mt. Jormajan on the northern section have the largest constrained area where there is overlapping of NIPAS lands, the permanent danger zone, pyroclastic flow hazard zones and areas with slope of 30%. Critical slopes can also be found in the Mt. Maraot Banwa in Cawayan, Tabon-tabon and Carrideo as well as in Salvacion adjoining Buenavista and San Isidro.  Other areas of critical slopes are in Casini near the boundary with Matnog and in hilly areas in Batang, Gumapia and Tongdol. The areas in the lower elevation at the valley floor that are prone to flooding during heavy rains are also considered under this category. The banks or easement of rivers and creeks are part of water bodies and are therefore constrained areas.    

Timberlands not yet declared as alienable and disposable lands in Tabon-tabon, Cawayan, Bolos and Liang with a total of 76.4970 hectares are also considered as constrained areas. Prime agricultural lands are the Network of Protected Agricultural Areas or Network of Areas for Agricultural Development (NPAA/NAAD) of Irosin that falls under ECA category. These are agricultural lands that are protected from any form of conversion so as to keep and preserve the highly suitable agricultural land for primary food crops. In this regard, the existing irrigated and potentially irrigable rice lands of 2,128.39 hectares of the municipality falls under this land resource category.

The total environmentally constrained area in the municipality is estimated to be 7,625.823 hectares which represents 51% of the total land area.