Gravel chub silt and debris. They are more often found in areas with limited macrophytes and larger root aquatic plants, algae and moss. Because of their need of a specialized clean habitats, the gravel chub is especially vulnerable to various forms of pollution, especially from agriculture practices that create erosion and excessive silt. In past sampling surveys the gravel chub had been found as far north in the Upper Iowa River as Le Roy, Minnesota, but because of excessive amounts of sewage, pesticides and sedimentation of rocks and sand, this is no longer the case. The presence of gravel chubs in a
Silt out which is also likely to disturb silt where it makes contact, and the underwater work may also disturb silt. For these reasons surface supplied divers must often operate in very poor visibility. Remotely operated underwater vehicles and submersibles manoeuver by using thrusters, and the water blast from thrusters has a similar effect to the wash from fins. Silt outs are dangerous situations for scuba divers, particularly in enclosed spaces or when there is no direct access to the surface (an overhead environment). Training courses in overhead environment diving, such as wreck or cave diving teaches various methods to cope with