A fluid for treating a subterranean formation includes a solvent, a rheology modifier, and a composition that includes a mixture of cellulose fibers and cellulose nanoparticles. The cellulose nanoparticles have a positive zeta potential in a range of about +100 mV to about +10 mV, and a length in a range of from about 50 nm to about 500 nm, and the cellulose fibers have a length from about 50 microns to about 500 microns.