1. What happened
Importing 'Unistorm' and 'AQUAS Water/River Set' A$ packages produces error:
"Assets/AQUAS/Scripts/AQUAS_LensEffects.cs(69,5): error CS0122: `UnityStandardAssets.ImageEffects.GlobalFog' is inaccessible due to its protection level"

Using Aquas package on its own or with some other packages reveals no such error.

2. How we can reproduce it using the example you attached
Resulting project is quite large, so not attaching.
Repro with importing 'AQUAS Water/River Set' (https://www.assetstore.unity3d.com/en/#!/content/52103) and 'Unistorm' (https://www.assetstore.unity3d.com/en/#!/content/2714). Import order is important! Importing Unistorm first won't reveal the issue.
Wait for import to be completed and script updated to be run.
Observe the Console.
Error: Assets/AQUAS/Scripts/AQUAS_LensEffects.cs(69,5): error CS0122: `UnityStandardAssets.ImageEffects.GlobalFog' is inaccessible due to its protection level

Same behaviour in 5.4.1p3 (1b587b7935dc)