The (strong?) electromagnetic fields from these cables must have some impact on marine systems, and I bet we don't well understand what that impact will be.

Years or decades later we may trace some significant change in marine systems back to this source, and then we may decide that the cost was much greater than the benefit. We have a habit of making decisions for short term gain and intentionally downplaying the potential risks...

Even short term, I wouldn't be surprised if Portugal felt the impact within one decade, as they are very dependent on fishing along their coast.