Linked from
The 6 pages that link to Kelvin's circulation theorem, each with the reason it gives.
VorticityRelated: Its conservation law connects circulation directly to the evolution of vorticity.
CurlRelated: It connects curl-related vorticity to circulation conservation in ideal fluids.
VortexRelated: It explains why ideal-fluid vortices can retain their circulation as they move.
Helmholtz's theoremsRelated: Conserved circulation underlies the conservation of vortex strength.