A lot of algae has grown in the pond.
Algae is floating on the surface of 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
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.
small pondweed; Potamogeton pusillus
spiny water nymph; spiny naiad; holly-leaved naiad
Phyllospadix iwatensis (a species of seagrass)
seaweed bed; seaweed forest