Illegal dumping is an act that has a serious impact on the environment.

Illegal dumping causes significant damage to the environment.

His actions exerted a great influence on our plans.

His opinion had a big influence on my decision.

That news greatly influenced his opinion.

This problem is very serious.

Do you understand the seriousness of this problem?

He crossed the border illegally.

His actions were clearly illegal.

His action is unforgivable.