Developing numeric nutrient criteria (NNC) is a data-driven exercise—from defining management goals to computing the final criteria. Importantly, decisions you make along the way must be supported by data that accurately characterize environmental conditions and responses. They are the foundation for developing effective nutrient criteria that result in healthy water environments that meet their designated uses.

• In the planning phase, you need data to support the selection of water body types and defining management goals. In this step, you begin to identify data of interest and their sources, and devise a plan for collecting and storing the data.
• In the problem formation phase, you need data to define assessment endpoints and guide your development of the conceptual model. In this step, you assess data to ensure key model components (or surrogates) are adequately represented.
• In the analysis phase, you analyze available data to inform criteria derivation.
• In the criteria derivation phase, you use results in weight-of-evidence analyses, interpretation, and consideration of downstream effects, as well as in the final criteria computation.

As you work through these phases, you will grow to appreciate that collecting, processing, and using data is an iterative process. You will likely revisit prior steps as you develop a deeper understanding of the relationship between causal and response variables and the role nutrient criteria can play in maintaining designated uses. Revising and refining data is not only acceptable but also encouraged as it usually results in stronger and more defensible criteria.