  We present a lattice calculation of the leading hadronic contribution to the
anomalous magnetic moment of the muon. This work is based on a subset of the
CLS ensembles with $N_f = 2+1$ dynamical quarks and a quenched charm quark.
Noise reduction techniques are used to improve significantly the statistical
precision of the dominant light quark contribution. The main source of
systematic error comes from finite size effects which are estimated using the
formalism described in Ref. [7] and based on our knowledge of the timelike pion
form factor. The strange and charm quark contributions are under control and an
estimate of the quark-disconnected contribution is included. Isospin breaking
effects will be studied in a future publication but are included in the
systematic error using an estimate based on published lattice results. Our
final result, $a_\mu^{\rm hvp} = (720.0\pm 12.4 \pm 6.8)\times 10^{-10}$, has a
precision of about 2%.
