Lama vs. lodo
In Portuguese, while both lama and lodo refer to wet, soft earth matter, distinct circumstances dictate which one to use. Lama refers to general mud formed by soil and water, usually caused by rain, whereas lodo refers to sludge, silt, or slime found at the bottom of bodies of water or in stagnant, damp environments.
Lama
B1Lama is the most common word for mud. It describes a mixture of earth, soil, or clay with water. You will use this word when talking about dirt roads after rain, dirty shoes, landslides, or pigs wallowing in the earth.
Depois da tempestade, o carro ficou atolado na lama.
(After the storm, the car got stuck in the mud.)
As crianças voltaram para casa cobertas de lama.
(The children came back home covered in mud.)
O porco estava feliz rolando na lama fresca.
(The pig was happy rolling in the fresh mud.)
Tire suas botas sujas de lama antes de entrar na sala.
(Take off your mud-dirty boots before entering the living room.)
Lodo
C1Lodo refers to muck, sludge, or silt. It is specifically the soft, dark, often smelly sediment found at the bottom of rivers, lakes, or sewage systems. It also refers to the slippery, green biological slime (algae/moss) that forms on rocks and walls in permanently wet areas.
Não gosto de nadar neste rio porque o fundo é cheio de lodo.
(I do not like swimming in this river because the bottom is full of muck.)
Tenha cuidado onde pisa, as pedras molhadas têm lodo e escorregam.
(Be careful where you step, the wet rocks have slime and are slippery.)
A equipe de limpeza removeu todo o lodo do fundo do tanque.
(The cleaning crew removed all the sludge from the bottom of the tank.)
O cheiro do lodo no porto era muito forte durante a maré baixa.
(The smell of the silt in the harbor was very strong during low tide.)
Summary
To choose correctly, look at the location and texture. If it is simply wet dirt on the ground caused by rain, use lama. If it is sediment underwater, toxic sludge, or slippery green slime on a wet surface, use lodo.