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The Fanghi Dam on the Rio Piscinas is located in the territory of Arbus, a few kilometers from the sea. This waterway, known as Rio Irvi-Piscinas, flows downstream from the historic Laveria Sanna, a plant linked to the Montevecchio Mine, and once transported the residual mud from the mining activity to the coast. This activity, necessary for the disposal of the waste, ended up in conflict with the centuries-old tuna fishing. Along the coasts of Sardinia, starting from Stintino, in the north of the island, it is still possible to observe several tuna traps, structures used for the seasonal catch of tuna; fishing took place mainly in spring, following the natural migratory cycle of Mediterranean tuna. These fish, coming from the Atlantic, crossed the Strait of Gibraltar and divided into two large groups. One headed towards the northern coasts of Africa, while the other followed the Spanish route. Once they reached the Balearic Islands, the tuna separated further: one part moved towards Sardinia, passing through Capo Pecora and continuing along the tuna fisheries of Portoscuso, Isola Piana, Calavinagra and Calasapone; the other continued towards the Gulf of Lion and the Ligurian coasts, dividing further. Some schools went down the western coasts of Corsica and then landed in Sardinia, touching places such as Vignola, le Saline, Pittinuri, Flumentorgiu (also known as Tunnaria), and finally Carloforte and Calasetta. Others, however, pushed towards the sea of ​​Tuscany, and then reached Naples and the northern coasts of Sicily.

This natural migration, so important for the economic activity of the tuna fisheries, could however be disturbed by mining waste discharged into waterways such as the Rio Piscinas or the Rio Naracauli. When tuna encountered these sediments along the coast, they tended to move away, drastically reducing the fishing opportunities for the tuna fisheries located further south.

This problem represented a serious economic damage for the fishing companies, who reacted by reporting the situation to the competent authorities. The protests, carried out at the Port Authority and the Mining Corps, pushed the authorities to force the mining companies to build containment basins along the rivers, with the aim of retaining the mud before it reached the sea. The construction of the Mud Dam on the Rio Piscinas, completed in 1941 by the Montevecchio company, fits into this context. A plaque still present on the structure reports the year of its construction, indicating it as the 19th century of the Fascist era; the dam remained in operation until 1973, the year in which it was destroyed by a violent flood.

The dam, in addition to its containment function, was equipped with a special mechanism that allowed the release of sediment to be regulated. A track ran along its crown, on which a wagon equipped with a winch moved. The system allowed the wooden “sheet piles” that held the mud to be lifted. At the end of the tuna migration season, the sheet piles were lifted, and the accumulated sediments were released into the sea. With the start of a new season, the sheet piles were repositioned, restoring the containment system to prevent the mud from interfering with the passage of the fish. This cycle was repeated every year until the Laveria Sanna plants were closed and the dam finally collapsed in 1973. Its collapse is a symbol of the decline of mining activity in the area.