Estanque vs. laguna vs. lago
In Spanish, describing a body of water depends heavily on its size, depth, and origin. While estanque, laguna, and lago can all be translated as pond or lake in various contexts, they represent a hierarchy from small and artificial to massive and natural.
Estanque
B2An estanque is a small cavity containing water that is usually artificial or man-made. It is typically used for ornamental purposes in gardens, for breeding fish, or for holding water for irrigation.
Mi abuelo construyó un pequeño estanque en su jardín para las carpas koi.
(My grandfather built a small pond in his garden for the koi carp.)
Las ranas hacen mucho ruido cerca del estanque por la noche.
(The frogs make a lot of noise near the pond at night.)
El agua del estanque se utiliza para regar los cultivos durante el verano.
(The water from the pond is used to irrigate the crops during the summer.)
Los niños disfrutan tirando monedas al estanque del parque.
(The children enjoy throwing coins into the park pond.)
Laguna
B1A laguna is a natural body of water that is generally smaller and shallower than a lago. Because it is shallow, sunlight can often reach the bottom, allowing plants to grow throughout it. It can refer to freshwater bodies or saltwater areas separated from the sea.
Vimos muchos flamencos comiendo en la orilla de la laguna.
(We saw many flamingos eating on the shore of the lagoon.)
Esta laguna es demasiado profunda para caminar, pero perfecta para nadar.
(This small lake is too deep to walk in, but perfect for swimming.)
El monuemento natural es una laguna volcánica de aguas verdes.
(The natural monument is a volcanic lagoon with green waters.)
El agua de la laguna se evapora rápidamente cuando hace mucho calor.
(The water in the lagoon evaporates quickly when it is very hot.)
Lago
A2A lago is a large, deep, and extensive body of water surrounded by land. It is distinct from a laguna because it is deep enough that water temperature varies by depth (stratification) and sediment does not easily settle at the surface.
El Lago Titicaca es uno de los lagos más altos del mundo.
(Lake Titicaca is one of the highest lakes in the world.)
Alquilamos un barco para cruzar el lago y llegar a la isla.
(We rented a boat to cross the lake and reach the island.)
La superficie del lago está congelada debido al invierno.
(The surface of the lake is frozen due to the winter.)
Este lago es tan grande que parece un mar tranquilo.
(This lake is so big that it looks like a calm sea.)
Summary
To choose the correct word, look at the origin and size. Use estanque for small, man-made ponds found in gardens or farms. Use laguna for natural, shallow bodies of water that are medium-sized. Use lago for vast, deep bodies of water like Lake Superior or Lake Geneva.