na-adjective
artificial; man-made; human-caused
Describes something caused or created by humans, often with a negative nuance when referring to errors or disasters. Used in formal and news contexts.
この湖は人為的に作られたものです。
This lake was artificially created.
事故の原因は人
The cause of the accident was human error.
自然的 means natural or spontaneous, the opposite of 人為的 in the sense of human-caused.
Compound of 人為 (human action) + 的 (-like, -ic). The exact historical derivation is uncertain, but the word follows a common pattern for forming adjectival nouns.