An aging asset in the Gulf of Mexico handles production from three main platforms that converge at an onshore treatment facility for oil and water separation. The water cut in this system is currently greater than 80%. Associated with the high water cut is a significant build-up of solids that are believed to contain potentially problematic microbes. Consistent with this concern recent in-line inspection results showed significant wall loss in one of the main lines coming to the onshore separation facility. Microbial characterization via quantitative PCR and DNA sequencing was performed on two of the platforms and at the separation facility to more fully understand the microbes present throughout the system and the potential risk they pose. In addition dynamic flow loop testing was performed using field production fluids to identify an optimized microbial control program. Biofilms grown in the flow loops were analyzed before and after treatment using 3-dimensional fluorescent microscopy that provided insight into the impact of the treatment program on the biofilm. Based on this testing a chemical treatment program was identified that showed excellent laboratory results. The modified treatment was implemented based on the lab testing and has been monitored in the field in three ways: water quality solids recovered following pig runs and quantification of microbes from a sessile monitoring device that was placed downstream of the modified treatment. To date the modified program has showed excellent success of minimizing biofilm build-up reducing solids recovered by pigging and improving water quality.