The Marine Environment Monitoring and Assessment National database (MERMAN) is a national database which holds and provides access to data collected under the Clean Safe Seas Environmental Monitoring Programme (CSEMP) formerly the National Marine Monitoring Programme (NMMP). The data collected are the responsibility of the Competent Monitoring Authorities (CMAs) who collect the samples from stations in UK waters using water sampling techniques, trawls, nets or grabs. The CMAs then send the collected samples to accredited laboratories where they are analysed. A weighting is calculated, based on the quality of the analysis. The weighting score incorporates the laboratory accreditation, reference material, inter-laboratory comparisons, detection limits, uncertainties and standard deviations. Where data do not meet a threshold score they are given a status of ‘FAIL’ and although they are stored they are not made available to external users. The MERMAN contaminants, nutrients, biological and eutrophication effects in water data start in 1999. Data are submitted by the CMAs annually and an annual submission may include updates to legacy data to provide additional data or improve data/metadata. The data held in MERMAN fulfils the UK's mandatory monitoring requirements under the Oslo and Paris Convention (OSPAR) Joint Assessments and Monitoring Programme (JAMP). These data are used in support of European Commission (EC) directives and national assessments, such as Charting Progress 2 and are also supplied to the European Marine Observation and Data Network (EMODNET).