To protect groundwater from further nitrate contamination, California regulations require dairy farmers to follow a strict nutrient management plan. The regulations require copious annual reporting of crop field management, farm infrastructure, and animal population. The data collected in these annual reports could be integral to evaluating and improving both farm practices and the regulations themselves. The objectives of this project were to (1) assess the reliability and accuracy of annual report data to allow the information to be used responsibly and (2) to suggest promising methods of improving data quality. Annual reports from 18 dairies were obtained to assess data reliability. Mass balance calculations were preformed to check the self-consistency of data within a facility. The results of mass balance calculations show that the annual reports do not account for a remarkably large percentage of the nutrients being produced on the farms. Literature suggests that over 60% of nitrogen (N) and 90% of phosphorus (P) should be recovered; however, a median of only 25% of both N and P in cattle manure was recovered based on annual reports. This could be due to many different causes including inaccurate nutrient sampling and analysis techniques or fraudulent reporting. It is likely that the sampling and analysis methods are a significant source of error because the accuracy of the majority of the protocols has not been assessed. The results of this study have led to projects that should improve data collection protocols in both the short and long-term. In the short term, online decision trees are being developed in collaboration with extension agents and consultants to help farmers self-assess their current data collection practices, and provide personalized suggestions for improvement. Suggestions are currently based on the recommendations of experts, but will be improved in the long term using a statistical modeling approach paried with field experiments to examine the uncertainty in each of the recommended protocols. With more reliable data, we can identify regulations and management practices that are more protective of groundwater quality.