MARÉ is a forensic intelligence system for marine litter that answers three questions no coastal municipality can currently answer: where did the litter on the beach come from, when will the next wave of debris arrive, and where to act upstream to prevent it. The solution combines inverse Lagrangian particle modelling over open oceanographic data from Copernicus Marine with AI-based visual classification of debris and independent biological validation through biofouling, triangulating ocean physics, computer vision and marine biology. For each beach, it returns a report with probable source zones, contribution percentages and 48-72h forecasts. The timing is favourable: Portugal spends an estimated €10-20M/year on reactive coastal cleanup with no source attribution tools, and the second cycle of the EU Marine Strategy Framework Directive (2027) makes source identification mandatory for Portugal's 30 coastal municipalities. The business model is annual B2G subscription (€8-50k/client: municipality, region, or national agency), targeting €1M in annual recurring revenue within 24 months in Portugal alone, with expansion to Spain and the EU Atlantic arc (~€20M). The team combines a marine biologist (Miguel Santos) and an AI analyst (Nuno Santos), a pairing that makes the methodology scientifically defensible and the product operational from day one. 100% open-data stack: Copernicus, OceanParcels, ERA5, TACO. No lock-in, no commercial dependencies.