Breeding takes place in late summer in burrows dug into the bank below the waterline. One large male occupies the burrow and defends the entrance; researchers studying the species call him the den-master. Multiple females may enter and spawn in the same chamber, so a single nest can contain eggs from several mothers, numbering in the hundreds.
The male remains after spawning. He fans the eggs to circulate oxygenated water, removes dead or fungal-infected eggs, and repels intruders, including other males that may attempt to eat the clutch. Parental attendance continues through hatching, which takes weeks, and larvae remain near the nest afterwards.
The species is often described as unchanged for millions of years, a claim that mistakes a conservative body plan for evolutionary stasis. What is documented is that the family Cryptobranchidae has a long fossil record, not that these animals are individually ancient survivors. Nesting burrows depend on natural earthen banks, which concrete channelisation removes.