California has immense biodiversity with ecosystems ranging from the highest and lowest elevations in the contiguous United States. Southern California, with a population nearing 28 million, also has a tremendous number of environmental stressors including urban stormwater runoff. This talk will describe the findings from regionwide ecological monitoring programs which assess the physical, chemical and biological health of the region’s 1,700 stream km and 36 coastal estuaries. Many of these monitoring and causal assessment tools can be applied in ecosystems outside of California. These programs address a variety of critical stormwater management questions including: 1) what is the extent and magnitude of ecological impacts? 2) Is the extent and magnitude of impacts getting better or worse with time? 3) What are the causes of ecological impacts? The answers to these questions are being used for management decision making such as which habitats are impacted and need restoration as well as which habitats are in good condition and need protection, creation of robust assessment tools to determine good sites from bad sites as well as tracking improvement in condition following remediation actions, and identifying stressors causing impacts to biological systems using new technology to save both time and money. The regional monitoring programs quantify many stressors including traditional pollutants, flow, physical habitat, bacteria and trash, amongst others.