Spawning of invasive smallmouth bass (Micropterus dolomieu) was studied in 2020 and 2021, in Lake Nojiri, Nagano Japan. Nest construction began once water temperatures reached 14 °C, and eggs progressed to fry dispersal in approximately two weeks. The main spawning season was in late May through early June, with a smaller second peak in late June through early July. Nests were constructed primarily under dock cover, and nest size and depth were positively correlated with male body size. Of the nests that received eggs, nearly all progressed successfully to fry dispersal. Time lapse videos of male guarding behavior revealed that as nests progressed, males rotated less and were suspended off the bottom substrate. Experimental removal of guarding males showed that freshwater gobies (Rhinogobius kurodai) were the only egg predators present and arrived on all nests in the egg stage. However, only a handful of gobies visited each nest and total egg predation was low. These results indicate that in Lake Nojiri, smallmouth bass spawning is highly successful and egg predators appear to have minimal effect on egg survival. The stable smallmouth bass fishery without stocking at this lake is likely a product of these favorable spawning conditions.