Repair of buildings and civil engineering constructions is a very important stage in their lifetime. By successfully planned and implemented repair procedure of building structures functionality for which they were constructed and original look can be restored. In the thesis I explored the repair procedure of reinforced concrete outlet channel of the Šmartinsko Lake. The result of repair, which began in 2008 and continued in 2013, did not meet the requirements of the designers of repair. Relatively soon after the completion of the construction works first defects were observed on the surface of the RC elements. The main problem in the repair procedure was poor condition of the original surface of the RC elements. The repair execution was further aggravated by further presence of back-water and extreme weather conditions. In the first part of the thesis the procedures of executed repair works are described. The second part is dedicated to errors that occurred because the contractor did not follow the instructions of designers of the repair procedure. At the end a proposal of better repair procedure is given. If this procedure was followed, the identified errors would probably not have occurred.