Ventura County Sheriff's deputies employed the ROV -- remotely operated vehicle -- after spotting a dark shape in the water, which they thought might be a body. After lowering the ROV, deputies discovered the object was a tree branch.

It's apparent how difficult the search is from the images ... divers can only see inches in front of them. Making matters even more difficult ... they don't know where Naya was when she disappeared.

The recovery effort was called off Friday night but will resume at first light Saturday.

As we reported, Naya and her 4-year-old son were swimming in Lake Piru Wednesday when she disappeared. Her son climbed back in the boat and told authorities he was swimming with his mom but she never got back on the boat.

In addition to the ROV, authorities are using side-scan sonar, dogs and divers to locate Naya's body.

The Ventura County Sheriff released security camera footage Thursday from the boat launch where Naya and her son rented a pontoon boat on the lake.

As we reported, more than 20,000 people have now signed a petition demanding that the dangers of Lake Piru -- with all the debris in the water -- be made clear to anyone who wants to boat or swim in the lake. Naya would be the 9th drowning victim at the Lake since the mid-'90s.