According to the SNIRH, on the last day of July, compared with the previous month, there was a decrease in the volume stored in all river basins monitored.

The basins of Barlavento (24.4 percent), Mira (46.4 percent) and Lima (48 percent) had the lowest water availability at the end of July.

According to data from the SNIRH, the basins of Mondego (82.7 percent), Guadiana (78.1 percent), Douro (76.3 percent), Tagus (75 percent), and Cávado and Oeste (both with 73 percent) had the highest levels of storage at the end of July.

The information made available also states that the July 2021 storages by river basin were higher than the July storage averages of the last 20 years (1990/91 to 2019/20), except for the Lima, Mira and Ribeiras do Algarve basins.

Each river basin may correspond to more than one reservoir.