The stability of tailings dams in long term perspective depends, amongst others, on the prevention of internal erosion, a process that results from an exceeding seepage pressure causing particles in a dam to migrate, with possible consequences of damage and failure of the dam construction. Therefore, a major questions for tailings dam design is: What maximum hydraulic gradient can we allow for a tailings dam construction in order to prevent internal erosion in a long term perspective, i.e. over a time period > 1000 years? With regard to this long term design of tailings dams, natural analogies to dam constructions are considered, i.e. formations from the last glaciation period that have fulfilled the task of damming water. Such structures are especially interesting with regard to their obvious stability against internal erosion over long time. Consequently, it is assumed that a critical hydraulic gradient exists, and that the material composition and compaction reaches an optimum which allows seepage without erosion. A literature study on critical hydraulic gradients is conducted. Relevant natural analogies to dam constructions are identified and analyzed with respect to the gradient. In addition, a case study on such a natural formation is carried out. Results on hydraulic gradients are then compared to current design guidelines for tailings dams in Sweden. Results of this study show that critical hydraulic gradients given in the literature range between 4,8 and 14 %, whereas gradients in long term stable natural formations are between 2 to 5 %. Current guidelines on tailings dam design in Sweden relate the maximum gradient to the internal angle of friction, thus resulting in gradients of about 12 to 27 %. With regard to long term stability, possible degradation and results from comparisons to long term stable natural analogies, a modification of the design criteria for Swedish tailings dams should be considered.