noun which may take the genitive case particle 'no'
freshwater; limnetic
Used attributively to describe organisms or products originating from freshwater environments. Often appears in scientific or commercial contexts.
この湖には多くの淡水産の魚が生息している。
Many freshwater fish inhabit this lake.
淡水産の真珠は海水産のものより安価なことが多い。
Freshwater pearls are often cheaper than saltwater ones.
海水産 means 'saltwater/marine (product/organism)', the counterpart to 淡水産.
Compound of 淡水 (fresh water) + 産 (product, produce). The exact historical derivation is uncertain, but the word is transparently formed from these components.