A lot of algae has grown in the pond.
We collected the seaweed washed up on the shore.
The algae has grown thick inside the fish tank.
藻 is the everyday, colloquial word for pond or river weed, whereas 藻類 is the formal biological classification term.
藻 (seaweed/algae) is pronounced identically to 喪 (mourning) but has a completely unrelated meaning, so context alone distinguishes them.
marimo; moss ball; lake ball
seaweed
scraps of seaweed
Ochromonas vischeri (golden alga)
whorl-leaf water milfoil
common hornwort; Ceratophyllum demersum · Analipus japonicus; a brown alga
waterwheel plant
bladderwort
eelgrass; Zostera marina
small pondweed; Potamogeton pusillus
Standard kanji spelling for aquatic plants and algae.
The kanji 藻 is a phono-semantic compound with 艹 (plant) and 喿 (sound). The reading も is the native Japanese word for algae and aquatic plants.
spiny water nymph; spiny naiad; holly-leaved naiad
Phyllospadix iwatensis (a species of seagrass)
seaweed bed; seaweed forest