  We have found Dirac nodal lines (DNLs) in the band structures of metallic
rutile oxides IrO$_2$, OsO$_2$, and RuO$_2$ and revealed a large spin Hall
conductivity contributed by these nodal lines, which explains a strong spin
Hall effect (SHE) of IrO$_2$ discovered recently. Two types of DNLs exist. The
first type forms DNL networks that extend in the whole Brillouin zone and
appears only in the absence of spin-orbit coupling (SOC), which induces surface
states on the boundary. Because of SOC-induced band anti-crossing, a large
intrinsic SHE can be realized in these compounds. The second type appears at
the Brillouin zone edges and is stable against SOC because of the protection of
nonsymmorphic symmetry. Besides reporting new DNL materials, our work reveals
the general relationship between DNLs and the SHE, indicating a way to apply
Dirac nodal materials for spintronics.
