How does it operate? Fish collected in the field by the Environment Agency are frozen on site and details are recorded on the National Fish Tissue Archive record sheet. Prior to chemical analysis they are homogenized in their frozen state and divided into sub-samples back in the laboratory. Both whole fish and cryoground homogenates are stored long term at -80°C as a resource for retrospective monitoring. About 10% of samples have been homogenised and analysed for one or more groups of chemicals, the rest are still intact whole fish, mostly roach of around 15 cm length (3-4 years old typically). The chemical results, together with other relevant information, are stored in a database.