Python uses conda-base tensorflow-gpu instead of conda environment installation

I want to create a virtual environment using anaconda for python 3 in which I can use a specific version of tensorflow-gpu.

My base conda python is 3.6.8 and the base conda tensorflow-gpu version is 1.10.1.
I want to create an environment with python 3.6.9 and tensorflow-gpu 1.11.0.
I am running Ubuntu 18.04.

To do this, I have been running the following code in my bash:

$ conda create --name test_env python=3.6.9
$ conda activate test_env

However, when I open a python console and check the tensorflow version it is instantly 1.10.1 which is the tensorflow-gpu version of my conda base environment.

Python 3.6.9 |Anaconda, Inc.| (default, Jul 30 2019, 19:07:31) 
[GCC 7.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import tensorflow as tf
>>> tf.__version__
'1.10.1'

The problem seems to only occur with the tensorflow package. Other modules like keras give the expected ModuleNotFoundError error when I try to import them after i created the test_env environment.

Even if I install a specific tensorflow version with the following command, the tensorflow version remains to be 1.10.1.

$ conda install tensorflow-gpu==1.11.0

When i use conda list it (only) lists the target tensorflow-gpu version:
tensorflow-gpu 1.11.0 h0d30ee6_0

Do you have any ideas on how to use tensorflow-gpu version 1.11.0 in a new virtual environment?

$ conda create --name test_env python=3.6 tensorflow==1.11