to use in normal conditions. Once the water level rises to the point where it crosses the bridge surface, the bridge is generally unsafe to use due to high current. The force of the moving water may be strong enough to physically push the vehicle off the bridge: the higher the percentage of the vehicle in the water, the more likely the water's force will take the vehicle off the bridge and send it downriver with substantial damage. An additional risk for trying to cross a bridge under water, especially when more than a couple of feet deep, is the possibility of the vehicle's engine stalling. As people will typically try to then get out of the vehicle, they may step into water currents that cause them to fall or be pulled down into the water. As the current during floods is often quite strong, it may sweep them downriver and carry them into debris, possibly causing injury or death. In developed countries this will usually be indicated by warning signs. An additional hazard is that the bridge surface may become completely obscured by the water, making it relatively easy to fall off the bridge surface into the deeper and more hazardous water on either side. As a consequence, the line of the submerged bridge is often marked with poles or other structures to indicate its course to unwary travelers and emergency users even when submerged. Despite the obvious dangers and warnings given there are still a significant number of emergencies and even deaths attributable to the unwary use of low-water bridges during flood conditions. One attempted solution/deterrent is the Stupid Motorist Law in the American state of Arizona. Drivers who become stranded on flooded low-water bridges are charged with the cost incurred by emergency services to come to their rescue. Fish passage at low-water crossings Since 1980, the ecological impact of road crossings on natural streams and rivers has been recognised. Baffles may be installed along the culvert to provide some fish-friendly alternative. But baffles can reduce drastically the culvert discharge capacity for a given afflux, thus increasing substantially the total cost of the culvert structure to achieve the same design discharge and afflux, or increasing the risk of road flooding in an existing structure. See also Floodway Ford External links/references Design of Irish bridges, fords and causeways in developing countries Low Flow, Mid-Level Stream and Ditch Crossings With