This study investigated the presence of microplastics (MPs) in the gastrointestinal tracts of four fish species from the estuarine Ciénaga Grande de Santa Marta (CGSM) in northern Colombia. Of the 140 fish purchased at a local market, 17 (12.1%) were found to contain MPs as confirmed by FT-IR analysis. Among the four different species, Mugil incilis (mullet) showed the highest MP prevalence with just over a fifth of the individuals containing MPs in their gastrointestinal tracts (10 out of 46 (frequency of MP occurrence in %) FO% = 21.7%). This was followed by Caranx hippos (crevalle jack, 2 out of 19 (FO% = 10.5%)), Caquetaia kraussii (yellow mojarra, 3 out of 35 (FO% = 8.6%)), and Eugerres plumieri (striped mojarra, 2 out of 40 (FO% = 5.0%)). From the 17 fish, only 19 MPs were found of which 17 (89.5% were fibers) and 2 (10.5%) were fragments. While polyester and polyethylene were the most common fibers, nylon, acrylic, polyethylene, and modacrylic were also identified suggesting a wide variety of origins and sources. These finding provide the first evidence of MP ingestion by resident fish species in Colombian estuarine waters. Since the region has been variously recognized as being of regional and international importance (i.e., RAMSAR site in 1998 and UNESCO Biosphere Reserve in 2000), we advocate the ongoing investigation of MP pollution in both the environment and biota.