Managing stormwater continues to be a priority for many urban regions across the United States due to environmental and public health regulations. At the same time, stormwater is becoming increasingly important as a potential source of local water supply in semiarid regions. In these drier climates, urban stormwater runoff often provides base flow in urban streams. In its raw form, this can be an environmental health hazard but also can provide beneficial uses (e.g., aquatic ecology, recreation, and irrigation water) once treated. The goal of the current work is to understand how implementing stormwater best management practices (BMP) to achieve water quality compliance standards affects the flow regime of an urban river. The Los Angeles River (LAR) is used as a case study because it represents a highly urbanized, semiarid system where engineered infrastructure defines the drainage system and compliance with federal water quality standards is a widespread issue. The US Environmental Protection Agency’s system for urban stormwater treatment and analysis integration (SUSTAIN) model with a stormwater management model (SWMM) hydrologic core is used to simulate scenarios of low-impact development (LID) BMPs to meet compliance. Results show that in order to meet requirements for metals in the LAR using BMPs, the following impacts on streamflow may result when utilizing LID BMPs: a reduction in dry-weather flows by about 45%, a reduction in peak flows by 10%–25% compared with recent historical values, and changes in the seasonal flow distribution. These findings have direct policy implications for optimizing beneficial uses of the LAR while meeting water quality standards necessary for public health.