On Sunday crews were using sonar to comb an area of the lake about 1 mile wide and 3 miles long, Utah County Sgt. Eldon Packer said.
"We still believe he is in the water," Packer said. "We feel confident that we've covered the area quite well, but at the same time, we haven't located him."
Family members who were watching the search effort from the shore on Sunday told police Huynh was an experienced fisherman who spent many hours on the lake. Based on information from family, police believe began his fishing expedition about 9 a.m. Saturday. His empty boat was not spotted until about 6:30 p.m.
"The boat was found in good condition," Packer said, adding that life jackets were found on board.
Crews from sheriff's office search and rescue team and the state parks were expected to continue the search effort until dark on Sunday and resume again Monday morning, Packer said.
Police are not yet ready to say Huynh is presumed dead. Packer added.
"But the longer we go ... we're over 24 hours now and at this point there's no sign of him any place," Packer said.