Global economic growth is placing unprecedented pressure on marine resources, though rising awareness of Blue Economy concepts has also driven governance toward protecting the ocean’s valuable resources and services. While the ocean economy accounts for 3% of the global gross domestic product, over half of the economy in the Caribbean city of Cartagena, Colombia, is associated with the sea. Cartagena’s main economic activities include the following: (i) beach and sea tourism, as Colombia’s principal destination; (ii) maritime transport, receiving thousands of ships annually from over 100 countries; (iii) a large coastal industrial sector, mostly petrochemical; and (iv) fisheries, traditionally supporting the livelihoods of coastal communities. However, marine pollution threatens the sustainability of many of these activities. Large sediment loads flowing from the Magdalena River create turbid plumes in the sea, impacting coral reefs, scuba diving, and beach esthetics. Sewage overflows following intense rainstorms occasionally contaminate beach waters, surpassing swimming standards for water quality. Wastewater discharges from the city’s industrial zone and from the upstream watershed contribute excessive nutrients and organic matter, resulting in hypoxic conditions in the marine ecosystem. Meanwhile, fish contaminated with metals such as mercury, chromium, and lead directly impact the health of local fisheries and their consumers. Decreasing fish stocks are exacerbated by increasing demographic and economic pressures leading to overfishing by artisanal fishermen, who despite these hardships have still demonstrated their willingness to pay for reducing pollution and improving biodiversity. To balance a sustainable Blue Economy, improved pollution regulations are needed to conserve these impacted marine resources and ecosystem services. Such policies should include the following: (i) ecologically relevant thresholds for the receiving marine ecosystems, (ii) a scientific foundation linking discharge limits with seawater quality, (iii) rigorous monitoring programs to ensure discharge compliance, and (iv) sound economic incentives that align societal interests with the incentives of those who generate the externalities. Economic valuations of local ecosystem services would further support governance by raising awareness of their crucial role in the city’s economy and social well-being. However, more research is needed to approximate the value of local ecosystem services, as a review of 67 studies from around the world showed that available estimates from other study areas (between $1 and $4.6 million per hectare per year) are too wide-ranging to be practically applied in local policy design. Therefore, it is necessary to engage local communities, urban residents, tourists, and tourism operators in valuation exercises to reach more accurate valuations of the social costs and benefits of steering Cartagena’s activities toward a more sustainable socio-ecological system.