Census Bureau map
|Location||Humacao, Puerto Rico|
|Area||0.139179 km2 (0.0537373 sq mi)|
|Length||0.6 km (0.37 mi)|
|Width||0.4 km (0.25 mi)|
|Highest elevation||34.9 m (114.5 ft)|
|Highest point||El Morrillo|
|Density||0 /km2 (0 /sq mi)|
The island measures 600 m (660 yd) north–south and 400 m (440 yd) east–west, including the flat northeastern peninsula, which is connected to the main part only by a narrow sandy isthmus. Six hundred meters west of the southernmost point is a shoal, Bajo Evelyn, which has a shallow depth of 8 fathoms. While the island is flat in the north, it reaches a height of 34.9 m (115 ft) 2.9 km (1.8 mi) southwest of the island's port, on a small rocky hill called El Morrillo, which rises abruptly from the water and the lowland around it. The area of the island is 0.14 km² (139,179 m²: Block 2000, Census Block Group 2, Census tract 1801, Humacao Municipio, Puerto Rico), of which the northeastern peninsula accounts for about 0.02 km². The island is part of Punta Santiago barrio of Humacao.
The island has a free-ranging population of about 950 Rhesus monkeys. The monkeys are the offspring of an original group of 409 monkeys imported from India in 1938 that were used for scientific research. Today, the island serves as a research center for the University of Puerto Rico Caribbean Primate Research Center, the National Institutes of Health, Yale University, and Harvard University. The station accommodates 11 researchers and technicians who take the short boat trip from Humacao on a daily basis and normally don't stay on the island.
Cayo Batata, the second island belonging to Humacao, is located 5.7 km to the southwest.