Human wastewater entering into bodies of water such as rivers or lakes can be dangerous because I. it causes a drop in the biological oxygen demand. II. it can lead to cultural eutrophication. III. the wastewater can carry pathogens.

Option-II and III

Explanation:

The wastewater produced by humans like from the human toilets is dumped into the flowing river bodies mostly in rivers and in the lakes also.

The human wastewater is rich in the nutrient contents like the phosphorus, nitrogen, and potassium. These nutrients could be accumulated in the lakes which could cause eutrophication in the lakes and rivers.

Also, the human stool sump is rich in the disease-causing pathogens like the bacterial species present in the gut and intestine.  

Thus, Option-II and III are correct.