To promote high-quality economic development, China continues to strengthen its network infrastructure, but it is unclear how this affects the regional ecosystem. To clarify the impact direction, based on the weekly data of river pollution in China from 2004 to 2018, this paper regards the Broadband China (BC) strategy as a quasi-natural experiment and uses a difference-in-difference (DID) model for empirical analysis. The study found that network infrastructure construction significantly exacerbates river pollution. After a series of robustness tests, such as the placebo test and propensity score matching DID (PSM-DID), this research conclusion still holds. The impact of network infrastructure construction on river pollution is more visible in economically developed regions as well as cities with a higher level of digital economy development. The mechanism analysis confirms that during the sample period, network infrastructure construction led to secondary industry agglomeration but did not have a significant impact on innovation ability or environmental regulation, thus leading to the continuous intensification of river pollution. This paper not only provides empirical evidence for the study of the environmental effects of network infrastructure construction but also provides suggestions on how to better weigh the relationship between economic development and the environment in the digital economy.