Manhattan Tuttle Creek Reservoir collects far more than water from its drainage basin, which stretches well into southeastern Nebraska.
The lake also collects all the silt and sediment carried into it by the Big Blue River sediment that one day will fill the lake and turn it into a giant mud flat.
The lake, which stretches northwest from Manhattan to Randolph, has already lost one-third of its original capacity since it was created in 1962, the Army Corps of Engineers said. A delta of sediment has already moved past the Randolph Bridge on Kansas Highway 16 near the northwestern tip of the lake.
Brian McNulty, the Corps' operations manager at Tuttle Creek, said current predictions point to the lake filling up in 2076 which is actually later than the Corps had originally estimated.
In Nebraska, the Big Blue River Basin begins just below the Platte River. It is about 110 miles wide at its widest point.
Other lakes in nearby basins have reservoirs upstream that catch sediment, McNulty said, but there are no upstream reservoirs in the Big Blue basin.
Also, he said, very little sediment is collecting on the lake bottom at Tuttle Creek. Instead, it has stayed near the northwest end to form a delta.
"Running water has the ability to move sediment," McNulty said. "When it gets to a still body of water, it loses its energy and drops."
The rate at which the delta of sediment is moving south toward the dam is slower than predicted both in 1968 and 1987.
When the dam was built, Corps officials predicted that 25 years later, in 1987, the sediment delta would have passed the Randolph Bridge. It's just now at that point this year.
But by 2012, McNulty predicted, roughly two-thirds of the original lake will be very shallow or covered in sediment.
Still, he said, the Corps has no plans to stop the lake from filling in.