The El Consejo Nacional de Vialidad said that work was complete on a 25-meter (82-foot) bailey bridge that spanned where the road was washed out.
The washout was at a stream bed called Quebrada Flores. Heavy rains earlier in the week took out the roadbed and two drainage lines.
This is considered an important tourism route because it is along Lake Arenal, and there is no alternate route, said the Consejo.
The site still is a mess with mud and gravel approaches to the temporary bridge. The Ministerio de Obras Públicas y Transportes urged caution on the part of motorists.
This is the first major washout of the new rainy season.