Sixty miles of river. Murky waters, thick mud and seemingly insurmountable piles of debris. Painstaking recovery efforts are still underway for around 100 people missing following the devastating July Fourth flooding along the Guadalupe River in central Texas. Stark images show search teams on their hands and knees sifting through two-story piles of debris from trees turned into sticks. The grim task, using strategies including hand-sifting and specific diving techniques, is expected to drag on for months. "We have a long, long way to go to really thoroughly search this area," said Capt. Max McQuarrie of the Virginia Beach Water Rescue Team, whose crew is assisting in Texas. "It's going to be a slow, methodical process … to really provide the answers that everyone's looking for." While many families are waiting for those answers, some have already learned their loved ones were among themore than 130 people who diedas a result of the floods. "More than 1,000 local, state and federal responders – in addition to thousands of volunteers from across the country – continue intensive search operations," Kerr County Emergency Operations Center Unified Command said Tuesday. Search teams run 7 a.m. to 7 p.m., with an hour break for lunch at noon, before heading back into the field, said Joe Rigelsky, a founder of Upstream International, a Christian nonprofit involved in the search. Credentialed search teams are eating "heavy in protein, good carb-load meals" – prepared by organizations like World Central Kitchen and Mercy Chefs – so they have the energy to do the work, he said. "Work teams come in shifts, but team leads – I haven't had a day off," said Rigelsky, who arrived July 4. The process can take an emotional toll, Michael Guyer, a volunteer who joined the search last week, told CNN. "The burnout is real," Guyer said. "For hours you'll be digging through piles of silt, mud, debris and rock. Typically finding nothing in frustration. Then the next hour or day you'll hear that someone in that very spot found bodies, and you think to yourself, 'If only I dug more, if only I had dogs, if only we had more manpower and equipment.'" Equipped with the limited resources of only a shovel and "our sense of smell," Guyer said, search conditions can be "miserable" at times. "There is so much sand, mud, debris and silt we are digging through that it takes hours to dig with just shovels," he said. Complicating matters, volunteerswere asked to vacatethe river area for their safety during inclement weather with the potential for renewed flash flooding earlier this week. The Upper Guadalupe River Authoritycontinues to advisethe public to avoid being near or in waterways in Kerr County "due to debris, fast-moving currents, and poor water quality." Areas to be searched range from nearby lakes to large piles of debris in residents' own front yards. Authorities in Kerrville say they are working on plans to remove water from at least one lake in their search for victims. They are seeing how feasible it would be to drain Nimitz Lake, which is overflowing a dam on the Guadalupe River, Assistant City Manager Michael Hornes said in a special city council meeting Monday. "Nimitz Lake is saturated, it's overtopping the dam, and it's going to continue as long as the rain continues," Hornes said, noting murky water and debris are making it difficult for searchers to see. Holmes said city, state and federal officials are working through several plans on how to safely pump water from the lake without causing additional issues upstream due to how saturated the soil is from recent rains. Back on land, many debris piles on private properties can't be reduced by hand and require heavy machinery. Kerrville officials are requiring professional search teams to check the piles before removing them. Officials have also warned residentsnot to burn debris pilesfor fear that remains may be trapped underneath. The searches are conducted in small, established search grids. Each section of the grid system is then meticulously documented – how often the section was searched, which assets were used and what the water levels were at the time of the search. McQuarrie's team has been working on a 10-mile section in the heart of Kerrville, which includes debris piles, islands and tributaries. The divisions are lettered from Alpha through Lima; some are smaller, some a little bigger, depending on how challenging the search areas are, McQuarrie told CNN. The Delta search area assigned to his team from Virginia includes four to five bridges, and six or seven low-head dams, each of which run their own challenges, according to McQuarrie, who noted water levels vary from very deep to very shallow. Downed trees, massive piles of rock and debris are found along both sides of the river, forming an entirely different landscape than the green pasture and land that once lined the banks. One section of the search area, where large amounts of rock and sediment are piled up, carried there by the "absolute force of nature" the Guadalupe swelled to on July 4, has been dubbed the "suck pile" by search and recovery crews, McQuarrie said. The pile, which varied in height, stretched at least 200 yards, he added. "We're dealing with areas that have anywhere from six to eight feet of new land," Rigelsky told CNN. "We've got areas that weren't islands before." Since their arrival a week ago, McQuarrie's team has been combing through their search area "looking, smelling, listening," he told CNN. The team starts with a primary search where they pick spots they want to go back over and mark those with cell technology. Then secondary searches are done, followed by targeted searches, which often include canine search teams and heavy equipment, like excavators. "Debris fields, in the early stages, may not have decomposing matter in them, so dogs might not pick them up. So, you may mark that as unsearchable, and then you come back with whatever equipment can make it searchable," Rigelsky explained. "It really has been a heavy dog-oriented search. The humans, the people involved, are only as good as the dogs they're with," Rigelsky said. Images sharedby the Center Point Volunteer Fire Department show a canine team, machine operators and a recovery crew working in unison to carefully search one of the many giant debris piles along the 60-mile stretch "layer by layer," the department wrote on social media. "What we're really focusing on now too, are the divers," Razor Dobbs with the Center Point Volunteer Fire Department toldCNN affiliate WFAA. "The divers now are being able to go in and really scour underneath the surface, because up on top of the land, it's been combed over … scores of times by human eyes, on foot, and also with the canine units." Once the solid layer of debris is cleared off the surface of the river, divers gear up and search the bottom and nooks below the surface, the fire department said. "There is a bit of risk to it, just because of visibility. We don't have any visibility at all, so everything is by feel," Dale Hammon, an experienced blackwater diver with a group of divers called 300 Justice Road,told CNN affiliate KBMT. For all the teams involved, safety is paramount. "We're trying to manage two really important things here, making sure we're all safe and getting home – and trying to be as diligent as possible, trying to cover it as best we can, making sure we leave no stone unturned, both literally and figuratively," McQuarrie explained. Retired Army Lt. Gen. Russel L. Honoré, who spent years working on disaster recovery operations with the military, including bringing relief to New Orleans after Hurricane Katrina in 2005, told CNN, "It's hard, tedious work." "In reality, we'll be finding remains for months and years to come," Honoré said, noting remains continued to be found six months after Katrina struck New Orleans. CNN's Ray Sanchez, Ed Lavandera, Ruben Correa, Isabel Rosales and Tori B. Powell contributed to this report. For more CNN news and newsletters create an account atCNN.com