[1][2][4] Existing populations are known from the Guadiana, Mira, and Sado Rivers in Portugal and Spain.

[4] Unio tumidiformis grows to a shell length of 57 mm (2.2 in) and wet weight of 16 g (0.56 oz).

[4] In a population in southern Portugal, mussels became sexually mature at the age of 2 years.

Its larvae (glochidia) seem to successfully develop only in fish of the genus Squalius (Cyprinidae).

This species is threatened by changes of hydrologic regime of the streams, natural droughts, gravel and water extraction, dams, and impoundments.