Wetlands are one of the most productive and fragile ecosystems on the Earth's surface. They have been providing essential services (irrigation, groundwater recharge, flood control and drinking water) to the society since the beginning of civilisation. The middle Ghaghara River basin is located in middle Ganga alluvial plain and is mainly drained by Ghaghara, Sarju, Rapti, Burhi Rapti and Kuwano rivers. In this study, Landsat 5 and 8 images of the post-monsoon months of 1989 and 2015 were used to extract the open water bodies of wetlands. Density slicing of the shortwave infrared band and the modified normalised water difference index (MNDWI) were utilised for the extraction of open water bodies. The total area of open water bodies was 472 km2 in 1989, while it reduced to 317 km2 in 2015. Thus, the reduction in open water bodies of wetlands is about 33%. Precipitation and temperature collectively play a major role in nurturing the wetlands. Therefore, in this study, trends in these climate parameters were analysed using non-parametric Mann-Kendall (MK) and Sen's slope methods. A significant increasing trend in annual mean temperature and a decreasing trend in total annual precipitation caused to shrink in open water bodies of the wetlands. Besides this, encroachment of cropland and built-up areas on wetlands denotes anthropogenic reason for the reduction in their areal extent. This study is beneficial to the planners and environmentalists for the restoration of shrinking open water bodies of wetlands in the middle Ghaghara River basin. © Springer Nature Singapore Pte Ltd. 2019.