What you're probably noticing
Maybe it's the smell in the laundry room that wasn't there last summer. Maybe it's the way the stucco near the foundation stays dark for days after a rain that ended a week ago. If you're near the canals, the marina, or one of the low-lying blocks south of Rose, you've probably also noticed standing water that doesn't drain the way it should, sitting in the yard or against the side of the house longer than seems normal. None of that is unusual for Venice. It's also exactly the pattern that leads to mold problems that homeowners don't catch until they're already extensive.
Why this stretch of coast behaves this way
Venice sits low, much of it near sea level, with a water table that's already close to the surface before a single drop of rain falls. The marine layer keeps humidity elevated most mornings, sometimes burning off by noon and sometimes not burning off at all in the winter months. Add the canals and the proximity to the ocean, and you have a neighborhood where the ground itself holds moisture longer than it does a few miles inland in places like Mar Vista or Culver City.
This matters for how water behaves after it lands. In a lot of the country, rain soaks in and moves on. Here, on the flatter lots and anywhere near the canal system, water can sit in yards and against foundations for days, especially after one of the heavier winter storms that roll through between December and March. That standing water doesn't need to enter the house to cause a mold problem. It just needs to sit close enough, long enough, for moisture to migrate through slab, stucco, or old subfloor.
More on this from Reading List Living Beside Standing Water And Keeping The House Dry.
The housing stock makes this worse, not better
A lot of Venice housing is old by California standards, plenty of bungalows and beach cottages from the 1920s through the 1950s, along with the denser infill and remodels that have gone up since. The older homes often have raised foundations with crawl spaces that were never properly vented or sealed, and slab additions bolted onto them later that create low points where water collects. Crawl spaces under these houses are a common place for moisture to sit unnoticed, because nobody looks under there until something smells wrong upstairs.
Newer construction isn't automatically safer. A lot of the infill built in the last twenty years uses slab foundations poured close to grade, sometimes closer than they should be given how flat and low this part of the city sits. If the original grading around the house didn't account for where water actually goes during a real storm, you can end up with a two-year-old house that has the same moisture problem as a seventy-year-old one.
What you can check yourself
Start outside. Walk the perimeter of the house after the next rain and look for water pooling against the foundation rather than running away from it. Check that gutters and downspouts actually carry water a few feet from the house instead of dumping it right at the base, which is a common and easy fix. If you have a crawl space, look for a vapor barrier on the ground and check whether it's intact, torn, or missing entirely.
Inside, pay attention to smell before you pay attention to sight. A musty smell in a closet, under a sink, or near an exterior wall usually shows up before any visible staining does. Check under sinks, around water heaters, and in the corners of rooms that share a wall with the yard where you noticed standing water. Peeling paint, bubbling drywall, or a slightly soft feel underfoot on flooring near an exterior wall are all worth noting, even if they seem minor.
Where this stops being a homeowner job
If you can smell mold but can't find it, that's the point to bring in someone who does mold inspection for a living. Mold likes to grow behind walls, under flooring, and inside crawl spaces, all places that are hard to check thoroughly without the right tools and without opening things up you'd rather not open up yourself. A proper inspection can include moisture meters and sometimes air sampling, which tells you things a visual check never will.
It's also worth getting an inspection any time you're buying a house in this part of Venice, even one that looks fine on a walkthrough. Standing water problems are often seasonal, so a summer showing won't reveal what a January storm would. And if you've already dealt with a leak or flooding once, even a small one, a follow-up inspection is a reasonable step before you assume it's handled. Mold that gets ahead of you here is a bigger job than mold caught early, and the coastal conditions that make Venice pleasant to live in are the same ones that make this an ongoing thing to stay ahead of, not a one-time fix.