  Spin-1/2 maple leaf lattice antiferromagnets are expected to show interesting
phenomena originating from frustration effects and quantum fluctuations. We
report the hydrothermal synthesis of a powder sample of bluebellite
Cu$_6$IO$_3$(OH)$_{10}$Cl as a first potential candidate. Magnetization and
heat capacity measurements reveal moderate frustration with a Curie-Weiss
temperature of $-35$ K, and a magnetic transition at $T_N$ = 17 K.
Surprisingly, the magnetic susceptibility and heat capacity above $T_N$ are
well reproduced by the Bonner-Fisher model, which suggests that a
one-dimensional spin correlation with a magnetic interaction of 25 K occurs in
the apparently two-dimensional lattice. This emergent one-dimensionality cannot
be explained by orbital ordering or dimensional reduction due to geometrical
frustration. We believe that there is an unknown mechanism to cause
one-dimensionality in the spin-1/2 maple leaf lattice antiferromagnet.
