 The changes in water flow and use caused by Hoover Dam 's construction and operation have had a large impact on the Colorado River Delta . The construction of the dam has been credited as causing the decline of this estuarine ecosystem . For six years after the construction of the dam , while Lake Mead filled , virtually no water reached the mouth of the river . The delta 's estuary , which once had a freshwater @-@ saltwater mixing zone stretching 40 miles ( 64 km ) south of the river 's mouth , was turned into an inverse estuary where the level of salinity was higher close to the river 's mouth . 
 The changes in water flow and use caused by Hoover Dam <a href='null_genetive' title='1'><mark>'s</mark></a>construction and operation <a href='been_done' title='2'><mark>have</mark></a> had a large impact on the Colorado River Delta . The construction of the dam <a href='been_done' title='3'><mark>has</mark></a> been credited as causing the decline of this estuarine ecosystem . For six years after the construction of the dam , while Lake Mead filled , virtually no water reached the mouth of the river . The delta <a href='null_genetive' title='4'><mark>'s</mark></a>estuary , which once had a freshwater @-@ saltwater mixing zone stretching 40 miles ( 64 km ) south of the river <a href='null_genetive' title='5'><mark>'s</mark></a>mouth , was turned into an inverse estuary where the level of salinity was higher close to the river <a href='null_genetive' title='6'><mark>'s</mark></a>mouth . 
The changes in water flow and use caused by Hoover Dam  construction and operation done had a large impact on da Colorado River Delta . Tdaconstruction of the dam done been credited as causing thdaecline of this estuarine ecosystem . For six yrs after the construction of the dam , while Lake Mead filled , virtually no water reached thedauth of the river . The data  estuary , which once had a freshwater @-@ saltwater mixin zone stretching 40 miles ( 64 km ) south of the river  mouth , was turned into an inverse estuary where the level of salinity was higher close to the river  mouth .