Nonradiative recombination in InGaN epilayers grown by metal-organic chemical vapor deposition has been investigated. Time-resolved photoluminescence measurements show that the nonradiative recombination is suppressed with the periodical dilute H-2 carrier gas. Space-resolved cathodoluminescence images indicate that clustered V-pits in hillock-like In-rich regions and scattered V-pits primarily contribute to the nonradiative recombination. The number and size of hillock-like In-rich regions as well as the density of scattered V-pits are effectively reduced by the periodical introduction of dilute H-2 carrier gas, leading to a significant reduction of the nonradiative recombination. Transmission electron microscopy shows that the basal plane stacking faults, which are considered as the origins of the hillock-like In-rich regions, can be suppressed by the introduction of dilute H-2 carrier gas.