  Dominating electron-electron scattering enables viscous electron flow
exhibiting hydrodynamic current density patterns such as Poiseuille profiles or
vortices. The viscous regime has recently been observed in graphene by
non-local transport experiments and mapping of Poiseuille profiles up to room
temperature. Here, we probe the current-induced surface potential maps of
graphene field effect transistors using scanning probe microscopy at room
temperature. We discover the appearance of{\mu}m large areas close to charge
neutrality, where the current induced electric field opposes the externally
applied field. By estimating the scattering lengths from the gate dependence of
local electric fields, we find that these areas exhibit a dominating
electron-electron scattering as expected for viscous flow. We map the
respective meandering electric fields and carefully rule out artifacts such as
by source-drain voltage induced local doping. Our results imply that viscous
electron flow is omnipresent in graphene devices, even at moderate mobility.
