The aim of the article was an analysis of water level influence on a filtration phenomena occurring in a model test embankment constructed from ash-slag. The model has formed in a hydraulic channel in semi-full technical scale (0.6 m high, 2.0 m long at the base, 1.0 m width). The research involved on observation of the model test behavior during controlled rising and lowering water level on upstream, downstream, as well as synchronous up- and downstream slope. Tests of selected geotechnical parameters of the material that was silt up on the downstream slope of the embankment due to water overflow through the crest, have been also performed. Studies and analysis carried out that ash-slag can be used as the construction material for dikes, because simultaneous rising and lowering of water level on both sides of the embankment caused no negative filtration effects. In case of hydraulic structure with only one side of water level, the investigated anthropogenic material has the unstable characteristics, requires a slope stabilization against negative filtration phenomena.