We analyze how the criminalization of migration has taken hold in the borderlands of Ecuador and Colombia from 2000 to 2022, despite the existence of progressive legal frameworks in those two countries that have historically allowed for relatively open borders and recognition of migrants’ rights. We use a historical and ethnographic approach to explore how criminalizing mechanisms have been implemented, showing that the criminalization of migration happened episodically. The criminalization of migration has been justified under the legal regime of migrant-smuggling statutes, and mechanisms of criminalization have been activated only at specific junctures to halt the growth of irregularized migrations from the Global South to the U.S. We go on to argue that border crossings por trocha, as unlawful river and land pathways are locally known, have served as a strategy for resistance to criminalization and have enhanced the expansion and refinement of illegal border economies and local livelihoods.