environmental
background
biological
canal
chemical
corrosion
creek
crime
dam
danger
dirt
dirty
drain
drainage
ecology
environment
factory
fern
filter
filtration
flowing
garbage
green
hazardous
health
industrial
lake
nature
pipe
pipeline
plant
pollute
pollution
pond
protection
reflection
river
rust
rusty
sanitation
sea
sewage
steel
storage
toxic
turbidity
ugliness
unhygienic
waste
water