CEUTA, Spain—Numerous recent illegal border crossers are still in Ceuta, and the Spanish exclave is straining under their presence.Authorities reported tens of thousands of people crossing into the city from Morocco starting on July 30, but the majority returned home.Ceuta’s border fence is now...

CEUTA, Spain—By Aug. 1, the beach where tens of thousands of illegal immigrants came ashore in Ceuta stood largely empty and patrol boats idled beside 550 yards of floating containment barrier that had gone up only that morning.But the impact of the mass influx...