Substantial damage was reported Sunday night following a structure fire at a night club in Storm Lake. The Storm Lake Fire Department was dispatched to the Oasis Night Club in the 200 block of East Railroad Street at approximately 11:36 p.m. Upon arrival, firefighters determined the interior had already filled with extremely dense smoke. The near-zero visibility conditions required the use of thermal imaging cameras to locate the blaze at the east of the building and extinguish it. It took the crews nearly two and a half hours to bring the fire under control. Damage to the structure is estimated at $100,000. The Storm Lake Police Department, Buena Vista County Emergency Medical Services and MidAmerican Energy Company staff also responded to the scene. The cause of the fire has not yet been determined, and the Iowa State Fire Marshal’s Office is assisting with the investigation.