Artificial lakes are man-made bodies of water created by humans for various purposes such as irrigation, water supply, hydroelectric power generation, recreational activities, and more. In this case, we need to identify the artificial lake among the given options, which are Kodaikanal, Kolleru, Nainital, and Renuka.

Kodaikanal (Tamil Nadu):
- Kodaikanal is a popular hill station located in the Dindigul district of Tamil Nadu.
- It is famous for its scenic beauty and pleasant climate.
- Kodaikanal has several natural lakes, including the Kodaikanal Lake, also known as Kodai Lake.
- The Kodaikanal Lake is not an artificial lake but a natural one. It was created by the accumulation of rainwater in a valley.

Kolleru (Andhra Pradesh):
- Kolleru Lake is one of the largest freshwater lakes in India, located in the state of Andhra Pradesh.
- It is a natural lake and serves as an important habitat for several migratory birds.
- Kolleru Lake is not an artificial lake.

Nainital (Uttarakhand):
- Nainital is a popular hill station located in the Kumaon region of Uttarakhand.
- It is known for its beautiful lakes, including the Naini Lake, Bhimtal, Sattal, and more.
- The Naini Lake in Nainital is a natural freshwater lake and not an artificial one.

Renuka (Himachal Pradesh):
- Renuka Lake is located in the Sirmaur district of Himachal Pradesh.
- It is the largest natural lake in Himachal Pradesh and is considered to be the embodiment of the goddess Renuka.
- Renuka Lake is not an artificial lake.

Therefore, among the given options, the artificial lake is not Kodaikanal, Kolleru, Nainital, or Renuka.