Castaic Lake's Danger Advisory Covers the Upper Lake. Winter Magic Is Scheduled for the Lower One.

On Thursday, Oct. 29, Los Angeles County Parks raised the harmful algae advisory at Upper Castaic Lake from warning to danger, the highest level. Every recreational boat, kayak and jet ski came off the water. Five weeks later, Friends of Castaic Lake has a lighted boat parade on the calendar. Both are true because Castaic has two lakes, and the state rates their water separately.

KHTS ran the news as "Castaic Lake" without naming a body of water. KTLA's report said the county acted because conditions at Upper Castaic Lake had gotten worse. The California Department of Water Resources tracks each reservoir in a status table, and it has two separate rows for Castaic.

Two Rows on One State Table

The DWR algal bloom page lists every State Water Project reservoir it monitors. Castaic Lake and Castaic Lagoon each get their own line.

Nearby reservoirs show how much the ratings differ. On the same table, Pyramid Lake, up the I-5, is at Warning and Quail Lake has No Advisory. Each body of water is tested and posted separately, even two that share a name and a parking area.

What "Danger" Takes Off the Upper Lake

According to KTLA, the Oct. 29 upgrade bars these watercraft from launching on Upper Castaic Lake:

• Kayaks
• Windsurfers
• Jet skis and other personal watercraft
• Water-ski boats
• Wakeboard and wake-surf boats

The county also told visitors to stay away from scum floating on the water or collecting along the shoreline. It advised against eating fish or shellfish caught in the lake and against using lake water for drinking or cooking. KHTS reported that filtering or boiling the water does not make it safe.

Dog owners face the most serious risk. County officials warned that in animals, exposure can cause convulsions and, in severe cases, death. DWR says dogs and small children are the most likely to be affected because of their size and because they tend to stay in the water longer. Animals also drink while swimming and lick their fur afterward. If your usual walk ends at the upper lake's shoreline, the advisory applies to that spot.

How the Upper Lake Got Here in 2026

This is the upper lake's third algae posting of the year. The difference this time is that boats are off the water too.

1. February. DWR's Castaic Lake recreation page carried an update dated Feb. 10, 2026, noting caution advisories on the lake.
2. June. SCVNews reported on June 9 that water-contact activities at Upper Castaic Lake were prohibited, while boating and fishing were still allowed. The Lower Lake was unaffected.
3. July. On July 16, Los Angeles County announced that water contact could resume at the upper lake under a Caution advisory. That release again said Castaic Lagoon and its swim beach were not affected.
4. October. A warning was already in place when the county moved it up to danger on Oct. 29 and banned all recreational watercraft from launching.

During the summer restriction, people could still fish from a boat on the upper lake. This time there are no boats on the upper lake, and the county has advised against eating any fish caught there. In both June and July, the county said in writing that the Lagoon was unaffected.

Why a Danger Posting Stays Up for Weeks

State guidance on algae advisories works on a two-week clock. DWR says testing continues after toxins are found. Posted advisories are not reduced until lab results show the bloom declining and toxin levels below the level of concern for two weeks. The California Cyanobacteria and Harmful Algal Bloom Network's response guidance sets the same rule for removing a posting entirely: all "No Advisory" criteria must be met for at least two weeks.

The guidance also shows how far toxin levels rose to reach Danger. It sets these levels in micrograms per liter:

The state describes this as voluntary guidance, not regulation. A posting is triggered when any one of the criteria is met. In the summer, the county took 37 days to go from the June 9 report to the July 16 return to Caution, and that included treatment of the lake. This time the upper lake is starting from a higher level, so any step down will run on the same two-week rule.

DWR also notes that wind and waves can move a bloom or concentrate it in different parts of a reservoir. That's why the status table is the place to check before a weekend at the lake. Last week's news story won't reflect changes since then.

Winter Magic Is Planned for the Lagoon

The Lagoon is where the December event happens. Friends of Castaic Lake and LA County Parks are holding Winter Magic on Saturday, Dec. 5, 3 to 7 p.m., at the Lower Lake's Paradise Cove, 32132 Castaic Lake Drive. The event page lists the following, and the event is free.

• Snow and Santa
• Holiday activities and a marketplace
• A lighted boat parade
• A free meal for each child who checks in

Families can pre-register through a link on the event page. Boat owners register separately using the lighted boat parade form. It welcomes kayaks and other eligible watercraft, and parade logistics will be sent to registrants. Students taking part in the mini-water-bottle drive have a Dec. 3 deadline.

Winter Magic follows the group's summer Moonlight Madness series, which wrapped in September after four Saturday-night events with 632 attendee visits and 115 boats, KHTS reported. Since the Lagoon has its own status, check the DWR table and the Friends of Castaic Lake page the week of the event. Those two pages will show any change before Dec. 5.

The Rest of a Lake Visit in November

With boats off the upper lake, more visitors will be on the shore. The county's Castaic Lake State Recreation Area page lists hiking and mountain-biking trails and picnic areas, and DWR counts more than seven miles of trails and 29 miles of shoreline. Plan around these limits:

• Closed Mondays and Tuesdays. The county says its regional parks are closed both days. California State Parks lists Castaic Lake hours as sunrise to sunset, Wednesday through Sunday.
• No camping. Castaic Lake's campgrounds remain closed until further notice because of damage from the Hughes Fire.
• Freeway work on the way there. Metro's I-5 North County Enhancements are under construction from the SR-14 interchange to just south of Parker Road in Castaic. The project adds HOV and truck lanes, auxiliary lanes, soundwalls and a replacement Weldon Canyon Bridge, with completion estimated for spring 2027. Metro scheduled a virtual community update for Nov. 4 covering traffic shifts and closure timelines, and the project page is where those updates are posted.

If you want to learn what algae blooms look like, DWR's list covers the basics: blue-green, white or brown particles in the water, streaks that look like spilled paint, mats or foam along the shoreline, and sometimes a smell like gasoline or fish. DWR adds that you can't tell whether a bloom is toxic just by looking at it. For the upper lake, the posted sign and the state table are the guides to follow.

If your home is near Castaic Lake, questions about the lake, the I-5 work and the Hughes Fire repairs come up when it's time to sell. Dan Regan Properties follows those local changes closely and can show you how they factor into your home's value. Get your free home valuation, and we'll walk you through what buyers are asking about on your side of the valley.