In its most recent muon-neutrino disappearance measurement at 810 km, the NOvA experiment observed a deviation from maximal mixing (sin²θ₂₃=0.5) at 2.6σ. This result is in tension with the 295-km baseline measurements of T2K, which are consistent with maximal mixing. We propose that θ₂₃ is in fact maximal, and that the disagreement is a harbinger of environmentally induced decoherence. The departure from maximal mixing can be accounted for by an energy-independent decoherence of strength Γ=(2.3±1.1)×10⁻²³ GeV.

In this talk, I will review the role of decoherence in neutrino oscillations, show the implications for long-baseline measurements of θ₂₃, and comment on the prospects for future tests.