The 7 m-wide Canal Oeste passes over a series of first-order, intermittent streams on hillsides on its way to irrigate the lowlands of Guanacaste, Costa Rica. Streams passing under lined portions of the canal have maintained intermittent flow, while those under unlined portions of the canal have become perennial, thus providing a unique opportunity to examine the impact of drastically altered hydrology on macroinvertebrate communities of dry forest streams. Macroinvertebrates were studied from the end of the dry season through a wet season. Macroinvertebrate recolonization of intermittent streams at the beginning of the wet season was rapid, led by small bodied taxa such as chironomids and oligochaetes with short life cycles and/or great tolerance for low oxygen and spates. As additional, less tolerant taxa arrived, most likely aerially from adjacent perennial streams, the fauna of intermittent streams progressively became similar to that of perennial streams of the area within 3-4 months of rewetting. The great resilience of the macroinvertebrate community is clearly demonstrated by its ability to adjust with few modifications to a complete switch from intermittent to perennial hydroperiod.