Every year, thousands of oysters and mussels are harvested from the Thau lagoon, a body of water in the Hérault region of southern France, and then sold in local markets. Researchers have recently discovered a chemical signature in the lagoon's sediments that does not come from natural marine sources. Instead, the high levels of copper found in the oysters' flesh and in the sediment are traced back to two human activities: the use of anti-fouling paints on boat hulls and the application of copper sulfate in nearby vineyards. These practices, deeply embedded in the local landscape, contribute to the accumulation of copper in the lagoon over time. Copper from anti-fouling paints gradually wears off the hulls of boats and enters the water with every journey. Meanwhile, rainwater runoff from vineyards carries copper sulfate into the canals and eventually into the lagoon. Once in the water, copper tends to bind with fine sediment particles rather than dispersing, making it difficult to remove. Over decades, these particles settle at the bottom of the lagoon, forming a kind of "chemical memory" that records the history of human activity in the region. Oysters, which filter water and mud to feed, absorb this copper into their bodies, where it accumulates over time and is not easily eliminated. The Thau lagoon is not a remote, untouched environment. It is a dynamic area surrounded by fishing and leisure ports, with vineyards on the surrounding hills contributing to the renowned Languedoc wine region. The copper found in the lagoon's sediments is not the result of natural geological processes but rather of long-term human influence. The layers of sediment act as a geological archive, preserving the history of agricultural and nautical practices. By studying these layers, scientists can trace changes in local farming and boating activities over time. What makes this pollution particularly concerning is its subtlety. Neither the anti-fouling paint nor the copper sulfate used in vineyards are widely seen as major environmental threats. Anti-fouling paint is a common product used by boat owners to prevent marine organisms from attaching to their hulls, while copper sulfate is a traditional agricultural treatment used to combat fungal diseases in vines, even in organic farming. These practices contribute to copper accumulation in the lagoon without obvious signs of environmental harm, making the issue difficult to detect through conventional monitoring. The copper ends up in oysters through their natural feeding behavior, highlighting the complex and often invisible ways in which human activity can impact the environment.