We give a precise microlocal description of the singular profile that forms in the long-time
propagation of internal waves in an effectively two-dimensional aquarium. We allow domains
with corners, such as polygons appearing in the experimental setups of Maas, Benielli,
Sommeria and Lam (Nature388:6642 (1997), 557–561). This extends the previous work of
Dyatlov, Wang and Zworski (Anal. PDE18:1 (2025), 1–92), which considered domains with
smooth boundary. We show that in addition to singularities that correspond to attractors in
the underlying classical dynamics, milder singularities propagate out of the corners as well.
