The struggle to adequately monitor the condition of waterbodies with limited financial resources is a challenge faced by water resource agencies worldwide. For a resource agency to adequately meet its obligations to monitor and assess the condition of its waterbodies it must provide information at both the site-specific scale and the scale of the entire resource. This dual obligation requires different monitoring strategies.

Traditional targeted monitoring (in which site locations are selected to meet specific monitoring goals) is essential for answering many key water quality monitoring questions (e.g., what is the condition of specific sites, how do site conditions vary seasonally and annually, where are the best and worst sites, what are the primary water quality problems at specific sites, what are the effects of specific watershed activities and/or BMPs).

Although this approach can generate much valuable water quality data, it is unable to provide information about the overall condition of large populations of resources (e.g., all streams, lakes or wetlands in a state) unless the monitoring entity is prepared to perform a complete census of the targeted resource. Site specific monitoring approaches are also unable to provide an objective context for interpreting the data they generate.  However, the perspective provided from this context is a necessary logical foundation for a sound monitoring program.

In the US, the need for a broader context for interpreting the results of targeted monitoring data has driven the development of alternate sampling designs at both the state and federal level. To meet this need, the U.S. EPA established its Environmental Monitoring and Assessment Program (EMAP), a long term research program designed to develop the tools and techniques needed for cost-effectively answering the fundamental status and trends questions in the Clean Water Act. The EMAP studies are based on a probabilistic survey design in which each sampling location represents a known proportion of the total resource of interest (e.g., percent of total stream length) with known statistical confidence. This design permits the inference of resource conditions for large geographic regions with a relatively small investment in sampling (Ringold et al. 1996, Olsen et al. 1999, Stevens and Olsen 2004). After completing assessments of the condition of Eastern lakes and the condition of wadeable streams in the Middle-Atlantic states, the EPA initiated a similar assessment of streams in the western states (WEMAP), which included a high density of sites in California.

For the first time in 2006, the state of California used data from a probability survey to derive the condition assessments of its perennial streams in its 305(b) report to the US EPA (Ode and Rehn 2005, California State Water Resources Control Board 2006).

These reports were developed to meet California’s obligation to monitor its compliance with the goal of biotic integrity stipulated under Clean Water Act §305(b). Prior to these report, the ABL has presented results of the Southern Coastal California intensification area (Rehn and Ode 2004), Northern Coastal California intensification area (Rehn et al. 2005) as demonstration projects.

As the EPA’s Western EMAP sampling effort ended in 2003, the EPA strongly encouraged western states to continue the EMAP monitoring approach in their own state monitoring programs. Two monitoring programs in the California State Water Resources Control Board, the recently established Surface Water Ambient Monitoring Program (SWAMP) and the Non-Point Source Program (NPS) expressed interest in probabilistic sampling.

In concert with (and with funding from) their counterparts in the EPA Region 9 Non-point Source Programs and Office of Water, NPS and SWAMP developed the California Monitoring and Assessment Program (CMAP) to provide an additional four years of statewide probabilistic sampling to support continued ecological condition assessments. The study designs used for these condition assessments were developed by the EPA’s Office of Research and Development. Since the state and federal NPS programs brought a strong interest in the relationship between non-point source pollution sources and aquatic life use, the sampling design was adapted to include an explicit stratification by landuse/ landcover.