Divers spent most of the day at the Uvas Reservoir and ended the day at the Chesboro Reservoir. They are the two reservoirs closest to Sierra's home.
Out of about 2,000 sonar images that the dive team honed in on, about a dozen produced curious objects that they wanted to rule out as potential evidence in this case.
Six divers from the sheriff's office are navigating the murky water of the reservoirs. They don't mind the heavy rain, but the whole team had to keep an eye out for lightning storms.
"We don't want to be bringing ourselves into a direct hazard with the lightning if it starts to come in that fast, so we're being very mindful of that," said Sgt. Brett Moore, a Santa Clara County Sheriff diver.
The search of Uvas involves checking out eight items of interest that was captured by a high-tech sonar device. On Thursday, divers ruled out five items of interest at Chesboro.
"They were a large rock formation, a grate over an inlet valve, and a lot of wood and tree stumps," said Lt. Dan Rodriguez from the Santa Clara County Sheriff's Office.
Each object deemed worthy of further investigation is relocated using GPS and if a dive of 40 to 100 feet is required, a cage is dropped in the water and acts as a familiar marker of sorts.
"We'll drop a cage down that we can see with the sonar and then we bring the cage closer and closer to the image that we're looking for until the divers have a very short distance ," said Sgt. Don Ray from the Santa Clara County Sheriff's Office.
The daylong dive operation at Uvas follows a month of searching both on land and in water. Each outing is an effort to find evidence that would bring home 15-year-old Sierra.
Moore has been working the case since day one.
"We're here to do a mission. We focus on the mission at hand and we don't get discouraged and we keep coming out," said Moore.
Sheriff deputies will also be out this weekend re-canvassing the area in Morgan Hill. Large community searches are also planned for both Saturday and Sunday.