Novel, agricultural habitats are increasingly recognised for the conservation opportunities they present. Rice fields show particular promise for waterbirds and 'wildlife-friendly' farming initiatives, but most work has focussed on conspicuous, well-known species and the value of flooding harvested fields to provide non-breeding habitat. The Australasian bittern (Botaurus poiciloptilus) is a cryptic, globally endangered waterbird that breeds in rice crops in the Riverina region of New South Wales, Australia. To assess the size of the population, we surveyed rice fields from 2013 to 2017 on randomly selected farms in the Murrumbidgee valley. Occupancy modelling yielded population estimates ranging from 368 to 409 for 'early permanent water' crops. With conservative estimates for the unsurveyed Murray region, and for fields with 'delayed permanent water', we suggest that in most years the Riverina's rice fields attract approximately 500–1000 individuals to breed, representing about 40% of the global population. Water allocations for irrigation drive the area of rice grown, with the total Riverina rice crop ranging from 5,000-113,000 ha during 2010–2019. Previously overlooked, rice fields can play an integral role alongside natural wetlands in the conservation of the Australasian bittern. Contraction of the ponding period to increase water use efficiency and the transition of Riverina irrigators to cotton farming are immediate threats to this population. We recommend trialling 'bittern-friendly' rice growing incentives, development of supportive policy and acknowledgement that some water allocated to agriculture in the Murray-Darling Basin can have explicit environmental benefits. The significance of rice fields to other cryptic wetland species should also be assessed.