The sources and fluxes of superGZK neutrinos , E > 10 ^ { 20 } eV , are discussed .
The fluxes of cosmogenic neutrinos , i.e .
those produced by ultra-high energy cosmic rays ( UHECR ) interacting with CMB photons , are calculated in the models , which give the good fit to the observed flux of UHECR .
The best fit given in no-evolutionary model with maximum acceleration energy E _ { max } = 1 \times 10 ^ { 21 } eV results in very low flux of superGZK neutrinos an order of magnitude lower than the observed flux of UHECR .
The predicted neutrino flux becomes larger and observable by next generation detectors at energies 10 ^ { 20 } -10 ^ { 21 } eV in the evolutionary models with E _ { max } = 1 \times 10 ^ { 23 } eV .
The largest cosmogenic neutrino flux is given in models with very flat generation spectrum , e.g . \propto E ^ { -2 } .
The neutrino energies are naturally high in the models of superheavy dark matter and topological defects .
Their fluxes can also be higher than those of cosmogenic neutrinos .
The largest fluxes are given by mirror neutrinos , oscillating into ordinary neutrinos .
Their fluxes obey some theoretical upper limit which is very weak , and in practice these fluxes are most efficiently limited now by observations of radio emission from neutrino-induced showers .