WFR responds to large structure fire at 1312 13 Ave SE at 1348 on Thursday. Crews found heavy black smoke coming form commercial shop building that contained 4 business. The fire had started in one business and then burnt into the attic. Crews quickly attacked the fire with an interior attack and used a large 2 1/2 inch hose attack line along with a piercing nozzle attack line to penetrate the steel siding. The fire was contained to the the back half of the building and did not get into the front 2 business, however they did have some smoke and water damage. The back 2 business were very heavily damaged from the fire. The building is still standing but a good portion is completely loss as of the structure. Crews also used the Ladder truck to get above the roof and use a penetrating nozzle to attack the attic fire. Crews were on seen for more than 4 1/2. No injuries were report. The business did not have any employees there at the time of the fire and was it reported by personnel from the neighboring business. The cause of the fire is under investigation. Watertown Police Department and the SD Highway Patrol assisted with the fire.