Type of tropical moist forest lying over a thick bed of acidic peat, over 60% of which occur in Indonesia and Malaysia. Typically contain water with very low pH (<4.0) that is stained brown due to the release of various organic compounds from the decaying peat and thus often referred to as blackwater swamps. Usually contain some permanent water but also flood seasonally. Highly biodiverse when in pristine condition, with many species found nowhere else on earth, though increasingly subjected to intensive drainage, burning and subsequent conversion to agriculture in recent decades.