The research conducted in settling ponds located in the coal basin in Upper Silesia (southern Poland), detected in one of them presence of the widgeon grass Ruppia maritima. Currently, it is the only inland site of this species in Poland. The widgeon grass creates underwater meadows in the shore zone of the settling pond and it grows in dense communities together with the common reed Phragmites australis in the coastal zone. Apart from these two plants, no other species were found. The morphological features of the vegetative and generative organs of the studied population of R. maritima is similar to those that have been reported from Europe. The bottom of the pond is atypical for R. maritima – it is covered by mine waste. The water of the settling pond has a high salinity and the water chemistry corresponds to the more natural environments that are inhabited by widgeon grass. This substitute habitat, which imitates the natural environment of R. maritima contributes to the good development of these species. However the studied settling pond offers unstable conditions due to the ongoing mining activity and requires permanent monitoring.