concurring.
I concur in the opinion and judgment of the Court. I add these observations because of some reservation about what may be perceived as the extent of its holding.
The case concerns the liability of the State for a boating accident that occurred on a man-made lake. The statute sounds simple enough: public entities are not liable for injuries caused by “a condition of any unimproved public property * * *.” N.J.S.A. 59:4-8. This statutory definition begs the underlying question of what caused the accident.
The ordinary person looking at this case would conclude that the terrible tragedy occurred because the auxiliary outboard motor of the fishing party failed to start. Nonetheless, we must look at possible concurrent causes of the tragedy. Causation sounds simple, but
[a]s every freshman student of tort law soon learns to his discomfort, “causation” is an inscrutably vague notion, susceptible to endless philosophical argument, as well as practical manipulation.
[Robinson, “Multiple Causation in Tort Law: Reflections on the DES Cases,” 68 Va.L.Rev. 713, 713 (1982).]
We have been particularly candid to equate causation with issues of policy. See People Express Airlines, Inc. v. Consolidated Rail Corp., 100 N.J. 246 (1985). It is not surprising, then, that both majority and dissent view the question of causation through different prisms of public policy. The dis*277sent says that (1) you could not have the lake without the dam; (2) the lake is surely unimproved property; and (3) since the lake would not exist without the dam, “[i]t follows that the dam, like the rest of the lake, should have the benefit of the immunity granted by the Legislature to unimproved property.” Post at 283.
But that the improvement created the natural area does not necessarily immunize all aspects of the improvement, i.e., the dam itself. For example, would the dissent reach the same result had the Troths been fishing from the dam and fallen from a slippery and cracked portion of the dam, of which dangerous condition the State had notice under N.J.S.A. 59:4-2b? I think not. On the other hand, I must agree with the dissent that the State does not become liable for a boating accident because it is a dam that has created a recreational waterway. But within these polar points are the allegations that an inadequate spillway created a hazard at the dam lip and that a faulty boom device failed to restrain the boat from the fall. As noted, the victim’s wife reached for this wire rope but was unable to hold on to it.
Were these conditions of improved property that caused the injury? At this point we must review again the structure of the Tort Claims Act. In suits against a public entity, such as the Division of Fish, Game and Wildlife, plaintiffs alleging negligence must first establish the predicates for liability and later avoid application of any provision granting the sovereign immunity.
In this case, plaintiffs predicate their cause of action on the unsafe condition of public property. N.J.S.A. 59:4-2. Liability based on this provision requires a demonstration that (1) a dangerous condition of public property (2) proximately caused plaintiff’s injury (3) in a way that was reasonably foreseeable (4) after the entity in charge of the property either had notice in time to protect against the condition or had created the condition through an employee acting within the scope of employ*278ment. Brown v. Brown, 86 N.J. 565, 575 (1981). Further, the agency’s action or inaction must be palpably unreasonable. Ibid.
The key phrase, “dangerous condition,” is defined in N.J.S.A. 59:4-1a:
“Dangerous condition” means a condition of property that creates a substantial risk of injury when such property is used with due care in a manner in which it is reasonably foreseeable that it will be used.
A “substantial risk” giving rise to a dangerous condition is “one that is not minor, trivial or insignificant.” Polyard v. Terry, 160 N.J.Super. 497, 509 (App.Div.1978), aff'd o.b., 79 N.J. 547 (1979). A plaintiff must advance enough facts to enable a jury of reasonable people to find that the condition was dangerous. Id. at 510.
Once those predicates for liability have been met, a public entity may avail itself of certain immunities set forth in the Code. These are affirmative defenses on which defendant has the burden of proof. Thompson v. Newark Housing Auth., 108 N.J. 525, 533 (1987). As noted, the immunity claimed here is granted to the public entity when an accident is caused by a condition of “unimproved public property.” Each party approaches the issue of causation, then, from a different thesis, plaintiff alleging that the lack of an effective boom on the dam or an inadequate spillway caused the injury and defendant alleging that the natural waterway caused the injury.
Such subtle issues of causation have been particularly troublesome to this Court. Kolitch v. Lindedahl, 100 N.J. 485 (1985), illustrates the difficulty. In that case, the majority of the Court held that the legislative act of posting a 50 mph speed limit sign at a dangerous curve in the road could not constitute a dangerous condition of property. Id. at 495. The State relied on its statutory immunity when making legislative decisions with respect to speed limits. N.J.S.A. 59:2-3b (“A public entity is not liable for legislative * * * action * * *.”). Justice Handler, in dissent, parsed the question of causation further. He said that it was too facile to regard the legislative act as *279subsuming the ministerial act of placement of the sign. Kolitch v. Lindedahl at 512-14 (Handler, J., dissenting). In other words, it may have been appropriate to state at the entry to the roadway that the legal speed limit was 50 mph, but it was particularly inappropriate to place the sign at a dangerous curve in the road, thus suggesting that 50 mph was a “safe” speed.
In Thompson v. Newark Housing Authority, supra, 108 N.J. 525, the Court concluded that the statutory plan and design immunity did not relieve the defendant, as a matter of law of liability, for failure to provide smoke detectors in public housing projects. Yes, the project was built in accordance with plans, but the plans had never adverted to the condition asserted.
In short, these immunities are not self-executing, nor are they self-informing. I cannot agree that just because the lake is a natural area, an accident at the dam site is necessarily immunized. And, I must disagree with the conclusion in the majority opinion that because “the ‘dangerous’ condition * * * would not have éxisted had the dam not been built,” it must be regarded as a condition of improved property. Ante at 271. That logic would apply as well if the allegation had involved upstream ice fishing and the plaintiff had fallen through the ice.
To sum up, the Union Lake recreation area is not “improved property.” But that is not the total answer to this case. As I see it, the plaintiff alleges that particular features of a physical improvement to property, i.e., the inadequate spillway or the defective boom, caused the injury. On these issues, I think that the plaintiff has presented at least triable issues of fact as to whether or not such were the cause of the injury as opposed to the rush of water of the lake itself, as the State contends by way of affirmative defense.
I am not at all certain that after the plaintiff has presented her proofs there will be a triable issue of fact as to whether the *280State had notice of a dangerous condition with respect to the spillway that could be held to have caused the accident in a way that was reasonably foreseeable. N.J.S.A. 59:4-3. The notice to the State from the Army Corps of Engineers was concerned with one problem and one problem only, the danger to downstream residents and property owners from a collapse of the dam. Too swiftly flowing water might erode the earthen dam. Hence, the references to human disaster contained in the Army Corps of Engineers report are largely irrelevant to the circumstances of this case. Congress specifically directed the Army Corps of Engineers to make the studies beginning in 1972 as a result of downstream tragedies in Rapid City, South Dakota, and Buffalo Creek, West Virginia. Act of Aug. 8, 1972, P.L. No. 92-367, 86 Stat. 507 (codified as amended at 33 U.S.C. § 467); H.R.Rep. No. 92-1232, 92d Cong., 2d Sess. 1, reprinted in 1972 U.S.Code Cong. & Admin. News 2916. The Buffalo Creek Dam disaster killed 125 people and caused $50 million in damages. Dam Safety: Hearings Before a Subcommittee on Government Operations, 95th Cong., 1st Sess. 1 (1977) (statement of Hon. Leo J. Ryan, Chairman of Subcommittee). Hence 33 U.S.C. § 467c required the Army Corps to take into consideration “the possibility that the dam might be endangered by overtopping, * * * [or the failure of] gates on conduits, or other conditions which exist or which might occur in any area in the vicinity of the dam.” (Emphasis added). The Army Corps gave notice to the State of potential failure of the dam, not danger to boaters.
But this is not the time to resolve trial issues. The plaintiff has the right to present her proofs on this issue and on the other issues presented in the case.