The effect of O implantation in crystalline Ge on the density of native point defects has been investigated through transmission electron microscopy and B diffusion experiments. Annealing at 650 C following O implants produces a band of defects (∼ 5–10 nm), compatible with GeO 2 nanoclusters (NCs). A clear shape transformation from elongated to spherical forms occurs within 2 h, concomitant with a transient enhanced diffusion of B. A large injection of self-interstitials from GeO 2 NCs, giving a vacancy undersaturation, and a long-range migration of self-interstitials are evidenced and discussed.